Prototype-based virtual in-line sparing

Details Prototype-based virtual in-line sparing Prototype-based virtual in-line sparing

1999-03-10

2003-03-18

Myers, Paul R. (Department: 2184)

Error detection/correction and fault detection/recovery

Data processing system error or fault handling

Reliability and availability

C714S710000, C711S202000

Reexamination Certificate

active

06535995

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to direct access storage devices and, more particularly, to skip-sector defect mapping in such devices.
2. Description of the Related Art
A computer direct access storage device (DASD), such as a magnetic disk drive, has one or more disk platters, each with a magnetizable layer on its surface. Digital data is recorded on a disk in the form of magnetic transitions spaced closely together. The disk surface area is divided into approximately equal-sized portions called sectors, which are further divided into blocks. Data is stored in a series of concentric or spiral tracks across the sectors of the disk.
Within a track, a sector includes a short servo track information area followed by a customer data area. The servo track information area typically includes a sector marker, track identification data, and a servo burst pattern, which are recorded at the time of disk manufacture and are used for positioning of a read/write head over the disk. The customer data area contains data recorded by a disk drive customer, or end user. Recording densities, both in terms of radial tracks per inch and linear density within a track, have reached a level that creates extreme sensitivity to imperfections such as media defects in the magnetizable recording layer. The media defects result in portions of the magnetizable media layer becoming unacceptable for use in recording the magnetic transitions.
One way of dealing with media defects is to perform a disk format operation at the time of DASD manufacture wherein surface analysis testing (SAT) identifies unacceptable, defective sectors and designates some sectors as spares. If additional good sectors become defective during subsequent operation of the DASD, then the defective sectors may be replaced by the spare sectors. In some conventional disk drives, an identification (ID) field is written on the disk prior to each sector during the format operation. The ID field contains specific information concerning the sector that follows, including a logical block address that identifies a cylinder, head, and sector that unambiguously identify the sector. A bit flag in the ID field identifies whether the sector is a defective sector or a spare sector. In this way, information about good sectors, bad sectors, and spare sectors will be known to the disk drive controller.
A technique to increase the capacity of disk drives is to use a no-ID format. This technique uses servo sectors in combination with a defect map to identify data sectors and completely eliminate the need for ID fields. The no-ID format frees up additional disk surface area for storage of customer data. In a no-ID disk drive, the logical block address (LBA) is the address of a logical block of storage that can be used by the disk drive customer. A physical block address (PBA) is the address of a physical block of storage on the disk. To store a block of data, the disk drive must perform a logical to physical address translation to take an LBA reference and derive the correct PBA from among the possible range of PBAs. The LBA-to-PBA conversion typically uses a defect map table that contains the defect information and is usually stored in memory of the DASD.
FIG. 1
illustrates the relationship between LBA and PBA.
FIG. 1
shows a PBA column
102
that lists the physical block addresses (PBAs) distributed across a disk, and also shows an LBA column
104
that lists the logical block addresses (LBAs), which comprise the data blocks that are available for storage of customer data. The
FIG. 1
configuration is provided for purposes of illustration only. Between the PBA column
102
and the LBA column
104
is an indication of the PBAs that are either spares or defects; spare blocks are designated by “S” and defect blocks are designated by “X”. The order of blocks in the PBA column
102
corresponds to the order of the blocks on the disk. The blocks in the LBA column
104
are numbered in the order of their availability to the disk user. Thus, it should be clear that the LBA column is numbered according to the PBA blocks, except that the S blocks and X blocks are skipped. As noted above, a reference from a data interface to an LBA must be translated into the proper PBA address to access the actual physical data stored on disk.
One way to implement the LBA-to-PBA translation is to define virtual tracks and virtual sectors, and to perform defect mapping with two tables, a virtual track (VT) table and a virtual sector (VS) table. A virtual track is defined as a contiguous set of data sectors that have a predetermined number of available sectors. Virtual tracks are numbered sequentially, regardless of their physical location. A virtual sector is defined as a sector that is not a spare sector or a defective sector and is contained within a virtual track. All virtual sectors within a virtual track are numbered sequentially.
FIG. 2
shows a received LBA
202
that is to be translated by a disk formatter or disk controller into a PBA that determines a disk drive cylinder, head, sector value for the data block referenced by the LBA. The disk formatter makes use of a VT table
204
that groups together LBAs having shared high order bits. The VT entries are index locations into a VS table
206
that lists the virtual skip sectors for all virtual tracks. That is, the index locations identify a group of skip sectors located on the virtual track corresponding to the index location. The skip sector entries in the VS table
206
pertain to skip sectors, which are sectors that are not available to store data, but are either defective sectors or spare sectors held for future use. For example, skip sectors in
FIG. 1
are identified with either an “X” or an “S”, referring to defective sectors or spare sectors, respectively.
In the
FIG. 2
example, the VT table
204
is indexed by virtual track number. The first entry in the VT table indicates that there are no skip sectors (either defect or spare) preceding the first track of the disk. The second entry in the VT table indicates that, for this example, two defect sectors precede the start of the second virtual track. Thus, the first virtual track includes two skip sectors. The next line in the VT table
204
indicates that a total of five sectors have been skipped before the third virtual track is reached. Thus, there must be three skip sectors in the second virtual track. Likewise, the third virtual track must not have any skip sectors because the number of skip sectors for the fourth virtual track is the same as for the third virtual track. That is, VT[
3
]=VT[
4
].
The VS table
206
shown in
FIG. 2
contains the skip sectors that are pointed to by offsets from the entries in the VT table
204
. That is, the first entry in the VT table is zero, so the disk controller will use a zero offset into the VS table, and therefore the PBA associated with the first skip sector in the VS table for virtual sectors in the first virtual track is the first entry in the VS table, which will be referred to as VS[
0
]. The second entry in the VT table
204
is a “2” and therefore the index of the first skip sector in the second virtual track is offset from the index of the first skip sector of the first virtual track by two. Thus, the disk formatter will step into the VS table
206
two lines following the VS[
0
] entry to point to the second following entry, and the first skip sector in the second virtual track is VS[
2
].
The VT table and VS table technique recognizes that the LBAs for neighboring defect blocks share most of their high order address bits, making redundant much of the information otherwise stored in a defect map. To reduce the amount of memory needed to store the defect map, the mostly redundant high order bits of the LBAs are used as indexes into the VT table
204
, whose entries act as pointers to locations in the VS table
206
. The entries in the VS table
206
contain only the low order LBA bits that correspond

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