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SEAGATE 1200 SSD PRODUCT MANUAL, REV. A 49
9.4 AUTO-REALLOCATION
Auto-Reallocation allows the drive to reallocate unreadable locations on a subsequent write command if the recovery
process deems the location to be defective. The drive performs auto-reallocation on every WRITE command. With each
write to a Logical LBA, the drive writes the data to a different physical media location. Physical locations that return
unrecoverable errors are retired during future WRITE attempts and associated recovery process.
This is in contrast to the system having to use the REASSIGN BLOCKS command to reassign a location that was
unreadable and then generate a WRITE command to rewrite the data. This operation requires that AWRE and ARRE are
enabled—this is the default setting from the Seagate factory.
9.5 PROTECTION INFORMATION (PI)
Protection Information is intended as a standardized approach to system level LRC traditionally provided by systems using
520 byte formatted LBAs. Drives formatted with PI information provide the same, common LBA count (i.e. same capacity
point) as non-PI formatted drives. Sequential performance of a PI drive will be reduced by approximately 1.56% due to the
extra overhead of PI being transferred from the media that is not calculated as part of the data transferred to the host. To
determine the full transfer rate of a PI drive, transfers should be calculated by adding the 8 extra bytes of PI to the transferred
LBA length, i.e. 512 + 8 = 520. PI formatted drives are physically formatted to 520 byte LBA’s that store 512 bytes of
customer data with 8 bytes of Protection Information appended to it. The advantage of PI is that the Protection Information
bits can be managed at the HBA and HBA driver level. Allowing a system that typically does not support 520 LBA formats to
integrate this level of protection.
Protection Information is valid with any supported LBA size. 512 LBA size is used here as common example.
9.5.1 Levels of PI
There are 4 types of Protection Information.
Type 0 - Describes a drive that is not formatted with PI information bytes. This allows for legacy support in non-PI systems.
Type 1 - Provides support of PI protection using 10 and 16 byte commands. The RDPROTECT and WRTPROTECT bits
allow for checking control through the CDB. Eight bytes of Protection Information are transmitted at LBA boundaries across
the interface if RDPROTECT and WRTPROTECT bits are nonzero values. Type 1 does not allow the use of 32 byte
commands.
Type 2 - Provides checking control and additional expected fields within the 32 byte CDBs. Eight bytes of Protection
Information are transmitted at LBA boundaries across the interface if RDPROTECT and WRTPROTECT bits are nonzero
values. Type 2 does allow the use of 10 and 16 byte commands with zero values in the RDPROTECT and WRTPROTECT
fields. The drive will generate 8 bytes of Protection Information (e.g. 0xFFFFFFFF) to be stored on the media, but the 8 bytes
will not be transferred to the host during a READ command.
Type 3 - Seagate products do not support Type 3.
9.5.2 Setting and determining the current Type Level
A drive is initialized to a type of PI by using the FORMAT UNIT command on a PI capable drive. Once a drive is formatted to
a PI Type, it may be queried by a READ CAPACITY (16) command to report the PI type which it is currently formatted to. A
drive can only be formatted to a single PI Type. It can be changed at anytime to a new Type but requires a FORMAT UNIT
command which destroys all existing data on the drive. No other vehicle for changing the PI type is provided by the T10
SBC3 specification.
Type 1 PI FORMAT UNIT CDB command: 04 90 00 00 00 00, parameter data: 00 A0 00 00
Type 2 PI FORMAT UNIT CDB command: 04 D0 00 00 00 00, parameter data: 00 A0 00 00
9.5.3 Identifying a Protection Information drive
The Standard INQUIRY data provides a bit to indicate if PI is support by the drive. Vital Product Descriptor (VPD) page 0x86
provides bits to indicate the PI Types supported and which PI fields the drive supports checking.
Note. For further details with respect to PI, please refer to SCSI Block Commands - 3 (SBC-3) Draft Standard docu-
mentation.