Real estate abstract
A hard disk drive utilizes hard disks that recover the historically
unused read/write space or real estate located in the load/unload
zone. Approximately one-half of the load/unload zone is recovered
and available for reading and writing operations by forming a first
or radially outermost read/write track beginning immediately adjacent
to the inner radial edge of the load/unload zone and proceeding
radially inward from there to the conventional location of first
tracks in the prior art. In another version of the invention, almost
the entire load/unload zone is recovered and available for reading
and writing operations by aligning the first track with the center
of the load/unload zone and proceeding radially inward from there
as described above. Both of these versions make significant additional
surface area on the disk available where, in the prior art, no data
was stored, thereby increasing the efficiency and storage capacity
of the hard disk drive.
Real estate claims
What is claimed is:
1. A method of increasing a data storage capacity of a data storage
medium, comprising: providing a data storage device with a rotatable
data storage medium having a recordable data storage area and a
load/unload zone that comprises a portion of the data storage area,
and a slider having a head for reading data from and writing data
to the data storage area; orienting the slider relative to the data
storage medium so that the slider has a positive pitch static attitude
defined by a trailing edge of the slider being closer to the data
storage medium than a leading edge of the slider, such that the
trailing edge approaches the data storage medium before the leading
edge, and thereby reduces contact between the leading edge and the
data storage medium; providing a landing pad on the slider adjacent
to the trailing edge for reducing direct contact between the slider
and the data storage medium; reducing a load velocity of the slider
to reduce damage to the data storage medium and thermal erasure
of data recorded on the data storage medium due to an impact between
the slider and the data storage medium, the load velocity being
defined by a rate at which the slider moves toward the data storage
medium; performing load/unload cycles with the slider on the data
storage medium during manufacturing of the data storage device prior
to any servo writing operations in the data storage area to remove
abnormalities present in the data storage area such that, if damage
to the data storage area occurs during this phase of manufacturing,
then a damaged portion of the data storage area is mapped out so
that no data is written in the damaged portion; and writing data
to and reading data from the load/unload zone of the data storage
area.
2. The method of claim 1, further comprising orienting the slider
relative to the data storage medium so that the slider has a biased
roll static attitude defined by a outer radial edge of the slider
being closer to the data storage medium than a inner radial edge
of the slider, such that the outer radial edge approaches the data
storage medium before the inner radial edge, and thereby reduces
contact between the inner radial edge and the data storage medium.
3. The method of claim 1, further comprising reducing a rotational
speed of the data storage medium when the slider is loaded and unloaded
with respect to the data storage medium to reduce damage to the
data storage medium and thermal erasure of data recorded in the
data storage area.
4. The method of claim 1, further comprising write-verifying data
when data is written in the load/unload zone to confirm that the
data written in the load/unload zone was written correctly.
5. The method of claim 1, further comprising providing error-correction-code
bytes in the load/unload zone and increasing a length of the error-correction-code
bytes to improve recovery of any data that is lost after being recorded
in the load/unload zone.
6. The method of claim 1, further comprising rounding corners of
the slider, the corners being located at intersections between the
leading and trailing edges and the inner and outer radial edges
to decrease contact stress between the slider and the data storage
medium.
7. The method of claim 1, further comprising providing the data
storage area with a thermally conductive underlayer to reduce thermal
erasure of data recorded in the data storage area when contact between
the slider and the data storage medium occurs.
8. A method of increasing a data storage capacity of a data storage
medium, comprising: providing a data storage device with a rotatable
data storage medium having a recordable data storage area and a
load/unload zone that comprises a portion of the data storage area,
and a slider having a head for reading data from and writing data
to the data storage area; orienting the slider relative to the data
storage medium so that the slider has a positive pitch static attitude
defined by a trailing edge of the slider being close to the data
storage medium than a leading edge of the slider, such that the
trailing edge approaches the data storage medium before the leading
edge, and thereby reduces contact between the leading edge and the
data storage medium; providing a landing pad on the slider adjacent
to the trailing edge for reducing direct contact between the slider
and the data storage medium; reducing a load velocity of the slider
to reduce damage to the data storage medium and thermal erasure
of data recorded on the data storage medium due to an impact between
the slider and the data storage medium, the load velocity being
defined by a rate at which the slider moves toward the data storage
medium; performing load/unload cycles with the slider on the data
storage medium during manufacturing of the data storage device prior
to any servo writing operations in the data storage area to remove
abnormalities present in the data storage area such that, if damage
to the data storage area occurs during this phase of manufacturing,
then a damaged portion of the data storage area is mapped out so
that no data is written in the damaged portion; writing data to
and reading data from the load/unload zone of the data storage area;
and specifying that the load/unload zone of the data storage area
is a last area written to by the head.
9. The method of claim 1, further comprising implementing a parity
sector in the data storage area to improve recovery of any data
that is lost after being recorded in the load/unload zone.
10. The method of claim 1, further comprising writing a first track
in the load/unload zone at an interface between the load/unload
zone and a remainder of the data storage area.
11. The method of claim 1, further comprising writing a first track
in the load/unload zone adjacent to a boundary of the load/unload
zone that is spaced apart from a remainder of the data storage area.
12. The method of claim 1, further comprising orienting the slider
relative to the data storage medium so that the slider has an approximately
zero skew angle defined by an angle between a centerline of the
slider and a tangent that is perpendicular to a radius of the data
storage medium, such that a size of the load/unload zone required
by the data storage device is reduced.
13. A method of increasing a data storage capacity of a disk, comprising:
providing a hard disk drive with a rotatable disk having a recordable
data storage area and a load/unload zone that comprises a portion
of the data storage area, and a slider having a head for reading
data from and writing data to the data storage area; orienting the
slider relative to the disk so that the slider has a positive pitch
static attitude defined by a trailing edge of the slider being closer
to the disk than a leading edge of the slider, such that the trailing
edge approaches the disk before the leading edge, and thereby reduces
a probability of contact between the leading edge and the disk;
providing a landing pad on the slider adjacent to the trailing edge
for reducing a probability of direct contact between the slider
and the disk; reducing a load velocity of the slider to reduce a
probability of damage to the disk and thermal erasure of data recorded
on the disk due to an impact between the slider and the disk, the
load velocity being defined by a rate at which the slider moves
toward the disk; performing load/unload cycles with the slider on
the disk during manufacturing of the hard disk drive prior to any
servo writing operations in the data storage area to remove abnormalities
present in the data storage area such that, if damage to the data
storage area occurs during this phase of manufacturing, then a damaged
portion of the data storage area is mapped out so that no data is
written in the damaged portion; orienting the slider relative to
the disk so that the slider has a biased roll static attitude defined
by a outer radial edge of the slider being closer to the disk than
a inner radial edge of the slider, such that the outer radial edge
approaches the disk before the inner radial edge, and thereby reduces
contact between the Inner radial edge and the disk; reducing a rotational
speed of the disk when the slider is loaded and unloaded with respect
to the disk to reduce damage to the disk and thermal erasure of
data recorded in the data storage area; write-verifying data when
data is written in the load/unload zone to confirm that the data
written in the load/unload zone was written correctly; providing
error-correction-code bytes in the load/unload zone and increasing
a length of the error-correction-code bytes to improve recovery
of any data that is lost after being recorded in the load/unload
zone; and writing data to and reading data from the load/unload
zone of the data storage area.
14. The method of claim 13, further comprising rounding corners
of the slider, the corners being located at intersections between
the leading and trailing edges and the inner and outer radial edges
to decrease a probability of contact stress between the slider and
the disk.
15. The method of claim 13, further comprising providing the data
storage area with a thermally conductive underlayer to reduce a
probability of thermal erasure of data recorded in the data storage
area when contact between the slider and the disk occurs.
16. The method of claim 13, further comprising specifying that
the load/unload zone of the data storage area is a last area written
to by the head.
17. The method of claim 13, further comprising implementing a parity
sector in the data storage area to improve a probability of recovery
of any data that is lost after being recorded in the load/unload
zone.
18. The method of claim 13, further comprising writing a first
track in the load/unload zone adjacent to at an interface between
the load/unload zone and a remainder of the data storage area.
19. The method of claim 13, farther comprising writing a first
track in the load/unload zone adjacent to a radial centerline of
the load/unload zone.
20. The method of claim 13, further comprising orienting the slider
relative to the disk so that the slider has an approximately zero
skew angle defined by an angle between a centerline of the slider
and a tangent that is perpendicular to a radius of the disk, such
that a size of the load/unload zone required by the hard disk drive
is reduced.
21. The method of claim 7, wherein the thermally conductive underlayer
is a silicon substrate.
22. The method of claim 15, wherein the thermally conductive underlayer
is a silicon substrate.
Real estate description
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates in general to improved utilization
of disk storage space in a hard disk drive and, in particular, to
an improved method and apparatus for recovering previously unutilized
load/unload zone real estate on the disks of hard disk drives.
2. Description of the Related Art
Generally, a data access and storage system consists of one or
more storage devices that store data on magnetic or optical storage
media. For example, a magnetic storage device is known as a direct
access storage device (DASD) or a hard disk drive (HDD) and includes
one or more disks and a disk controller to manage local operations
concerning the disks. The hard disks themselves are usually made
of aluminum alloy or a mixture of glass and ceramic, and are covered
with a magnetic coating. Typically, one to six disks are stacked
vertically on a common spindle that is turned by a disk drive motor
at several thousand revolutions per minute (rpm).
A typical HDD also utilizes an actuator assembly. The actuator
moves magnetic read/write heads to the desired location on the rotating
disk so as to write information to or read data from that location.
Within most HDDs, the magnetic read/write head is mounted on a slider.
A slider generally serves to mechanically support the head and any
electrical connections between the head and the rest of the disk
drive system. The slider is aerodynamically shaped to glide over
moving air in order to maintain a uniform distance from the surface
of the rotating disk, thereby preventing the head from undesirably
contacting the disk.
Typically, a slider is formed with an aerodynamic pattern of protrusions
on its air bearing surface (ABS) that enables the slider to fly
at a constant height close to the disk during operation of the disk
drive. A slider is associated with each side of each platter and
flies just over the platter's surface. Each slider is mounted on
a suspension to form a head gimbal assembly (HGA). The HGA is then
attached to a semi-rigid actuator arm that supports the entire head
flying unit. Several semi-rigid arms may be combined to form a single
movable unit having either a linear bearing or a rotary pivotal
bearing system.
The head and arm assembly is linearly or pivotally moved utilizing
a magnet/coil structure that is often called a voice coil motor
(VCM). The stator of a VCM is mounted to a base plate or casting
on which the spindle is also mounted. The base casting with its
spindle, actuator VCM, and internal filtration system is then enclosed
with a cover and seal assembly to ensure that no contaminants can
enter and adversely affect the reliability of the slider flying
over the disk. When current is fed to the motor, the VCM develops
force or torque that is substantially proportional to the applied
current. The arm acceleration is therefore substantially proportional
to the magnitude of the current. As the read/write head approaches
a desired track, a reverse polarity signal is applied to the actuator,
causing the signal to act as a brake, and ideally causing the read/write
head to stop and settle directly over the desired track.
In hard disk drives, load/unload (L/UL) designs are used to "load"
the slider down from a ramp onto the spinning disk prior to any
data reading and writing operations, and "unloaded" off
of the disk back onto the ramp when the reading and writing operations
are complete. As shown in FIG. 1, the area of contact on the disk
surface is typically located adjacent to the outer radial edge 11
of the disk 13 and is known as the "load/unload zone"
15. Since the contact of the slider 17 with the disk can damage
the disk, the load/unload zone 15 is not used to store data or for
reading and writing operations. Load/unload zone 15 extends inward
for a prescribed radial distance Z to an inner radial position 19.
The first (radially outermost) read/write track 21 is located radially
inward of inner radial position 19. Additional read/write tracks
25 are located radially inward of first track 21. Load/unload designs
reduce the problems of head-disk stiction and media damage from
shock as the fly height (e.g., the height at which a slider flies
above the surface of a spinning disk) continues to decrease. These
designs also have the advantage of reducing power consumption.
However, as stated previously, L/UL schemes potentially risk media
damage from slider-disk contact during loading and/or unloading
due to high disk speeds and high load/unload speeds. Research has
shown that this damage is specifically associated with the sharp
corners and/or edges of the block-like sliders digging into the
disk surface upon impact. The resulting damage in the L/UL zone
of the disk makes this region unsuitable for data storage, thereby
reducing the overall storage capacity of the drive by 5 to 15%.
Thus, an improved method and system for overcoming these problems
to better utilize the L/UL zone is needed.
SUMMARY OF THE INVENTION
One embodiment of a hard disk drive apparatus and method constructed
in accordance with the present invention utilizes hard disks that
recover the historically unused read/write space or real estate
located in the load/unload zone. Approximately one-half of the load/unload
zone is recovered and available for reading and writing operations
by forming a first (radially outermost) read/write track beginning
immediately adjacent to the inner radial edge of the load/unload
zone and proceeding radially inward from there to the "conventional"
location of first tracks in the prior art. In an alternate embodiment
of the present invention, almost the entire load/unload zone is
recovered and available for reading and writing operations by aligning
the first track with the center of the load/unload (L/UL) zone and
proceeding radially inward from there as described above. Both of
these embodiments make significant additional surface area on the
disk available where, in the prior art, no data was stored, thereby
increasing the efficiency and storage capacity of the hard disk
drive.
The problem of disk damage during L/UL is reduced by designing
the air bearing, suspension, ramp, and disk drive parameters (e.g.,
disk and L/UL speeds) such that head-disk contact is eliminated
or reduced. Alternatively, the slider itself can be processed in
such a way that any contact that does occur causes no damage or
an acceptably small amount of damage to the disk. Rounding, which
also is referred to as "blending," slider corners and/or
edges so that no sharp points (regions of high stress concentration)
are presented to the disk surface during contact, is a demonstrated
way to reduce disk damage from L/UL. Slider corner and/or edge rounding
may have the added benefit of reducing disk damage associated with
mechanisms other than L/UL, such as reading or writing in the presence
of operational shock, disk defects, or particles. By reducing the
severity of slider-disk impacts, corner and edge rounding can additionally
reduce particle generation in the drive, and thereby improve drive
reliability. Yet another benefit results from rounding, smoothing,
or chamfering the rough, saw-cut edge of the slider and removing
any poorly-attached particles that would otherwise be released into
the drive upon contact.
The foregoing and other objects and advantages of the present invention
will be apparent to those skilled in the art, in view of the following
detailed description of the preferred embodiment of the present
invention, taken in conjunction with the appended claims and the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
So that the manner in which the features and advantages of the
invention, as well as others which will become apparent, are attained
and can be understood in more detail, more particular description
of the invention briefly summarized above may be had by reference
to the embodiment thereof which is illustrated in the appended drawings,
which drawings form a part of this specification. It is to be noted,
however, that the drawings illustrate only an embodiment of the
invention and therefore are not to be considered limiting of its
scope as the invention may admit to other equally effective embodiments:
FIG. 1 is a schematic plan view of a portion of a conventional
disk used in a prior art disk drive;
FIG. 2 is a schematic plan view of one embodiment of a hard disk
drive constructed in accordance with the present invention;
FIG. 3 is an enlarged schematic plan view of a portion of a first
embodiment of the hard disk drive of FIG. 2 and is constructed in
accordance with the present invention;
FIG. 4 is a schematic plan view of a portion of a second embodiment
of the hard disk drive of FIG. 2 and is constructed in accordance
with the present invention;
FIG. 5 is a schematic side view diagram of a slider and disk used
in the hard disk drive of FIG. 2;
FIG. 6 is a schematic end view diagram of a slider and disk used
in the hard disk drive of FIG. 2;
FIG. 7 is a schematic plan view of a portion of another configuration
used by the hard disk drive of FIG. 2 and is constructed in accordance
with the present invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
Referring to FIG. 2, a schematic drawing of one embodiment of an
information storage system comprising a magnetic hard disk file
or drive 111 for a computer system is shown. Drive 111 has an outer
housing or base 113 containing a plurality of stacked, parallel
magnetic disks 115 (one shown) which are closely spaced apart. Disks
115 are rotated by a spindle motor assembly having a central drive
hub 117. An actuator 121 comprises a plurality of parallel actuator
arms 125 (one shown) in the form of a comb that is pivotally mounted
to base 113 about a pivot assembly 123. A controller 119 is also
mounted to base 113 for selectively moving the comb of arms 125
relative to disks 115.
In the embodiment shown, each arm 125 has extending from it at
least one cantilevered load beam or suspension 127. A magnetic read/write
transducer or head is mounted on a slider 129 (shown schematically)
and secured to a flexure that is flexibly mounted to each suspension
127. The read/write heads magnetically read data from and/or magnetically
write data to a data storage area of the disks 115. The level of
integration called the head gimbal assembly is the head and the
slider 129, which are mounted on suspension 127. The slider 129
is usually bonded to the end of suspension 127. The head is typically
pico size (approximately 1250.times.1000.times.300 microns) and
formed from ceramic or intermetallic materials. The head also may
be femto size (approximately 850.times.700.times.230 microns) and
is pre-loaded against the surface of disk 115 (in the range two
to ten grams) by suspension 127.
Suspensions 127 have a spring-like quality which biases or urges
the slider air bearing surface against the disk to enable the creation
of the air bearing film between the slider and disk surface. A voice
coil 133 housed within a conventional voice coil motor magnet assembly
134 (top pole not shown) is also mounted to arms 125 opposite the
head gimbal assemblies. Movement of the actuator 121 (indicated
by arrow 135) by controller 119 moves head gimbal assemblies radially
across the data storage tracks on the disks 115 until the heads
settle on the target tracks. The head gimbal assemblies operate
in a conventional manner and always move in unison with one another,
unless drive 111 uses multiple independent actuators (not shown)
wherein the arms can move independently of one another.
Drive 111 employs a load/unload (L/UL) design in which the slider
129 is loaded down from a ramp (not shown) onto the spinning disk
115 prior to any data reading and writing operations, and unloaded
off of the disk back onto the ramp when the reading and writing
operations are complete. As shown schematically in FIG. 3, the area
of contact on the surface of disk 115 is typically located adjacent
to the outer radial edge 311 of the disk 115 and is known as the
"load/unload zone" 315. The load/unload zone 315 extends
radially inward for a prescribed radial distance Z to an inner radial
position 319. However, the load/unload zone 315 also may be located
at a radially inward position (not shown) adjacent to the hub 117
(FIG. 2) of the disk 115 rather than the outer radial perimeter
or boundary of the disk 115. Since the contact of prior art sliders
with conventional disks can damage the disks, historically the load/unload
zone is not used to store data or for reading and writing operations.
However, with the method and apparatus of the present invention,
the load/unload zone 315 is available for such operations.
In one embodiment of the present invention (FIG. 3), the first
read/write track 321 is located in the load/unload zone 315 at an
interface between the load/unload zone 315 and a remainder 316 of
the data storage area, or slightly radially inward from the interface.
The interface is defined as the area of disk 115 that is located
at the intersection between the load/unload zone 315 and the remainder
316 of the data storage area. Thus, with respect to the first read/write
track 321, the slider 129 "straddles" the interface such
that an inner radial portion of slider 129 is located over the remainder
316, and an outer radial portion of slider 129 is located over load/unload
zone 315, as shown, as data is read from or written to track 321.
Other read/write tracks are located radially inward of the first
read/write track 321.
In another embodiment of the present invention (FIG. 4), the first
read/write track 421 is located in the load/unload zone 415 adjacent
to a boundary 418 of the load/unload zone 415 that is radially spaced
apart from a remainder 416 of the data storage area. In the version
shown, this is approximately at the radial center of the load/unload
zone 415, or slightly radially inward of the radial center. The
radial center is defined as that portion of disk 115 that is located
about half way between the inner and outer radial boundaries 420,
418 of load/unload zone 415. Thus, with respect to track 421, the
slider 129 is located entirely or almost entirely over the load/unload
zone 415, as shown, as data is read from or written to track 421.
Other read/write tracks are located radially inward of the first
read/write track 421, some of which are also located in the load/unload
zone 415.
A number of component level and file level control parameters are
used to facilitate accomplishment of the present invention in recovering
at least a portion of the load/unload zone for data read/write operations.
For example, at the component level, the slider may be oriented
relative to the disk so as to have a positive pitch static attitude
(PSA). As shown schematically in FIG. 5, a positive pitch static
attitude is defined by a trailing edge 501 of the slider 129 being
closer to the data storage medium 115 than a leading edge 503 of
the slider 129 when the slider is not in a "flying" state.
In this configuration, the trailing edge 501 is inclined at an angle
.phi. to approach the data storage medium 115 before the leading
edge 503, and thereby reduce the probability of contact between
the leading edge 503 and the data storage medium 115. Orienting
the slider 129 at a positive PSA reduces the risk of damaging the
data storage medium 115 while allowing data operations in the load/unload
zone.
Another component level parameter that enhances the success of
reading and writing data in the load/unload zone is providing at
least one landing pad 505 (FIG. 5) on the slider 129 adjacent to
or at the trailing edge 501. With the landing pad 505 in this position,
the landing pad 505 reduces the probability of direct contact between
the slider 129 and data storage medium 115. If contacts do occur,
the landing pad 505 tends to make contact the data storage medium
115 rather than the slider 129 itself and thereby reduce the probability
of damage to the data storage medium 115. The details of implementing
this parameter are disclosed in U.S. Pat. No. 5,796,551 to Samuelson,
which is incorporated herein by reference.
One of the file level variables of the present invention includes
controlling the load velocity of the slider 129. The load velocity
is defined by a rate at which the slider 129 moves toward the data
storage medium 115. In one implementation, the load velocity is
reduced from typical prior art load velocities to approximately
15 mm/second to reduce damage to the data storage medium 115 and
thermal erasure of data recorded on the data storage medium 115
due to an impact between the slider 129 and the data storage medium
115. Additional details regarding thermal erasure are discussed
in the paper, Magnetic Erasures Due to Impact Induced Interfacial
Heating and Magnetostriction, by M. Suk, et al, Transactions of
the ASME, Vol. 122, January 2000, which is incorporated herein by
reference.
Another file level parameter that reduces the risk of damage to
the data storage medium 115 while performing data operations in
the load/unload zone is a manufacturing bum-in cycle. With this
parameter, load/unload cycles are performed with the slider 129
on the data storage medium 115 during manufacturing of the data
storage device 111 prior to any servo writing operations in the
data storage area. These cycles remove abnormalities present in
the data storage area and on the slider 129 such that, if damage
to the data storage area occurs during this phase of manufacturing,
then a damaged portion of the data storage area is mapped out so
that no data is written in the damaged portion.
The present invention also utilizes a number of optional parameters
which can significantly affect the performance of read/write operations
in the load/unload zone. For example, at the component level, the
slider 129 can be oriented relative to the data storage medium 115
so that the slider 129 has a biased roll static attitude. As shown
in FIG. 6, the biased roll static attitude is defined by an outer
radial edge 601 of the slider 129 being closer to the data storage
medium 115 than an inner radial edge 603 of the slider 129. In this
way, if contacts do occur, the outer radial edge 601 is inclined
at an angle .theta. to contact the data storage medium 115 before
the inner radial edge 603, and thereby reduce contact between the
inner radial edge 603 and the data storage medium 115. This forces
all of the potential damage to occur at the outer radial periphery
of the load/unload zone aligned with the outer radial edge 601 of
the slider 129. Thus, the probability of data damage due to mechanical
damage to the data storage medium 115 or thermal erasure within
the region radially inward from the outer edge of the load/unload
zone is significantly reduced.
In addition, a slider 729 (dashed lines) may be oriented at a skew
angle a (FIG. 7) that is non-zero. The skew angle a is defined as
the angle between a centerline 736 of the slider 729 and a centerline
734 of the slider 129 that is perpendicular to radii of the data
storage media 115. In FIG. 7, the leading outer radial corner 730
of slider 729 is radially aligned with the outer edge 718 of the
load/unload zone 715. Skewing the slider 729 increases the size
of the load/unload zone because of the increased radial profile
of the slider 729 relative to the media 115. Thus, the size of the
load/unload zone is reduced and the data storage area is effectively
increased by designing a system with approximately zero skew at
the load/unload zone, as shown by slider 129 in FIG. 7.
Several other optional but significant parameters at the file level
of control include reducing a rotational speed of the data storage
medium 115 from rotational speeds typically used in the prior art
when the slider 129 is loaded and unloaded with respect to the data
storage medium 115. Like the previous parameters, this process reduces
damage to the data storage medium 115 and thermal erasure of data
recorded in the data storage area. Another variable is to write-verify
data when the data that is written in the load/unload zone to confirm
that the data written in the load/unload zone was written correctly.
If the data is written incorrectly and the same area continues to
fail record, then the same area can be mapped out so that data is
not written to the same area in the future.
Yet another parameter is to provide error-correction-code (ECC)
bytes in the load/unload zone that are longer than conventional
ECC bytes that one skilled in the art would provide in the remainder
of the data storage area. The load/unload zone typically has no
ECC bytes since data is not normally written there. However, with
the present invention, ECC bytes are used in the load/unload zone
and they are longer than normal so that if any data is lost, more
of the lost data can be recovered. This enhancement improves recovery
of any data that is lost after being recorded in the load/unload
zone. Furthermore, if data is recovered with ECC bytes, the system
can be designed to map out the same region so that the data is moved
to another location and data is no longer recorded in the same area
in the future.
The present invention also includes a number of optional parameters
that are more difficult to implement, but can have a dramatic affect
on the performance of the data storage device when data is read
from or written to the load/unload zone. These parameters include
rounding the corners of the slider 129 (see FIGS. 5 and 6). Rounding
the corners of the slider located at intersections between the leading
and trailing edges 503, 501, and the inner and outer radial edges
603, 601, decreases contact stress between the slider 129 and the
data storage medium 115. Details regarding this parameter are disclosed
in U.S. Pat. Nos. 6,069,769, and 5,872,686, both to Dorius, et al,
which are incorporated herein by reference.
Another parameter includes providing the data storage area with
a thermally conductive underlayer 605 (FIG. 6), silicon substrate,
or like substrates with similar thermal diffusivity to reduce thermal
erasure of data recorded in the data storage area when contact between
the slider 129 and the data storage medium 115 occurs. The thermally
conductive disk underlayer 605 reduces the potential for thermal
erasure. In contrast, conventional glass substrates have low thermal
conductivity, which results in localized heating when the slider
contacts the disk. Substrates or thick underlayers 605 that are
thermally conductive remove heat away from the point of contact
quickly, thus the temperature at the contact point cannot rise high
enough for thermal induced erasure of data. See the "Transactions
of the ASME" paper, described above. Similarly, the slider
material can be made of softer material, more thermally conductive
material like silicon, and materials that would lead to a generally
smoother finish in order to reduce the likelihood of damage and
thermal erasure. Yet another parameter comprises specifying that
the load/unload zone of the data storage area is a last area written
to by the head, or remapping the logical block address (LBA), which
would further reduce errors in the load/unload zone.
Finally, a parity sector may be implemented in the data storage
area to improve recovery of any data that is lost after being recorded
in the load/unload zone. See, e.g., U.S. Pat. No. 5,745,453, to
Ikeda, which is incorporated herein by reference. In loading and
unloading on data, an error mechanism is introduced that is independent
of the writing and reading of data. This means there is no correlation
between when the sector was last accessed and when an error may
be induced. In such a situation, on track parity by itself is not
reliable. With on track parity (or any other type of error correction),
the system has a maximum capacity to correct m errors. That means
that the error must be detected prior to exceeding m errors on the
track. It is possible that there are >m errors on a track due
to multiple independent error events (different 1/ul incidents)
and the data is not recoverable. This can occur since there is no
correlation between 1/ul and reading data in the affected area since
there could be years between reads. Thus, it is insufficient to
just have parity on the track.
As an example, a parity system can be instituted where there is
1 parity sector per 4 data sectors (with or without interleaving).
If any given "event" hits only one sector of this parity
set (due to clever interleaving, or small defect size), there is
a finite probability that another such event will hit this track
again (it is known to happen on this track). This hit could also
be in this parity set. Interleaving does not change this, since
5 sectors is a constant percentage of a track no matter how arranged.
A solution to this problem is to create the parity sets including
data from out of harms way. Each parity set is limited to one sector
in the 1/ul zone, thus any number of errors in the 1/ul zone will
always be corrected (other error mechanisms aside). This is more
of a "radial" parity arrangement, where the parity set
comprises at least 2 tracks. In situations where the error mechanism
is not coupled to the access mechanism, data scrubbing is required.
Data scrubbing involves the reading and testing of the parity sets
to ensure validity (a standard solution in RAID, memory systems,
etc.). The concept is to force a correlation between error incidents
and accesses. In this case, the parity sets must be checked before
the number of errors on a track is likely to exceed m. Any errors
found during scrubbing are corrected from the parity. The downside
to data scrubbing is the performance hit: there is still a problem
with multiple-revolutions for writes, plus down time to do the scrubbing.
The trick with data scrubbing is when and how often to do it. In
RAID systems, it is done in the background during idle times. In
RAID the purpose of scrubbing is to guarantee fault tolerance. If
a parity set has an error, it can still be recovered. However, the
data may not be recovered if one of the drive fails. Therefore,
without data scrubbing, the array is not fault tolerant.
In the present case, the frequency and timing of scrubbing depend
on the application and the error generation details. Unfortunately,
there may not be any "idle" time in a non-traditional
application. For example, when a picture is taken with a digital
camera, the drive is spun up, the data written and then the power
is shut off. This leaves no opportunity for background scrubbing.
The only way to be sure that it takes place is to force it to occur
either before accepting data from the camera, or before posting
"write complete." Either way, the delay time is required
for performing the scrub. In a music device (e.g., MP3), the situation
is similar. Unless the drive is performing the power management
and buffering, the host will just spin up, read what is needed,
and shut off the drive.
The amount of performance that is lost due to scrubbing depends
on how much scrubbing is needed per incident. If any 1/ul event
can cause errors, then a scrub is needed after every load. The number
of tracks that need scrubbing depends on determination of the landing
location. The entire zone may need to be scrubbed. A "best
case" (no errors found) scrub requires [period*number_tracks*number_heads].
The number of tracks appears to be a significant fraction of the
drive (>1%), otherwise it would not be worthwhile to put data
in the zone. For example, if there are 100 tracks*2 heads at 3600
rpm, 3.2 seconds are required to perform the scrub. Although this
solution solves the data integrity issue if the scrubbing frequency
is high, the performance cost is very high.
The present invention has several advantages. A hard disk drive
apparatus and method constructed in accordance with the present
invention utilizes hard disks that recover the historically unused
read/write space or real estate located in the load/unload zone.
Approximately one-half of the load/unload zone is recovered and
available for reading and writing operations by forming a first
read/write track beginning immediately adjacent to the inner radial
edge of the load/unload zone and proceeding radially inward from
there to the "conventional" location of first tracks in
the prior art. Alternatively, almost the entire load/unload zone
is recovered and available for reading and writing operations by
aligning the first track with the center of the load/unload (L/UL)
zone and proceeding radially inward from there as described above.
These embodiments make significant additional surface area on the
disk available where, in the prior art, no data was stored, thereby
increasing the efficiency and storage capacity of the hard disk
drive.
The problem of disk damage during loading and unloading operations
is reduced by designing the air bearing, suspension, ramp, and disk
drive parameters, such that head-disk contact is eliminated or reduced.
Alternatively, the slider itself can be processed in such a way
that any contact that does occur causes no damage or an acceptably
small amount of damage to the disk. Rounding, which also is referred
to as "blending," slider corners and/or edges so that
no sharp edges are presented to the disk surface during contact,
is a demonstrated way to reduce disk damage from L/UL. Slider corner
and/or edge rounding may have the added benefit of reducing disk
damage associated with mechanisms other than L/UL, such as reading
or writing in the presence of operational shock, disk defects, or
particles. By reducing the severity of slider-disk impacts, corner
and edge rounding can additionally reduce particle generation in
the drive, and thereby improve drive reliability. Yet another benefit
results from rounding, smoothing, or chamfering the rough, saw-cut
edge of the slider and removing any poorly-attached particles that
would otherwise be released into the drive upon contact.
While the invention has been shown or described in only some of
its forms, it should be apparent to those skilled in the art that
it is not so limited, but is susceptible to various changes without
departing from the scope of the invention. |