Seagate (ST16000NM002G) - Инструкция по эксплуатации - Страница 40

Seagate Exos X16 SAS Product Manual, Rev. K

39 

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Defect and error management

9.6

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 sectors 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.

9.6.1

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 inter face 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 RDPROTEC T  and WRTPROTEC T  fields. The  drive will generate 8 bytes (e.g.0xFFFF) 8 bytes of Protection

Information 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.

9.6.2

Setting and determining the current Type Level 

A drive is initialized to a type of PI by using the format 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. PI Types cannot coexist on a single drive. A drive can only be

formatted to a single PI Type. It can be changed at anytime to a new Type but requires a low level format 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 CDB command: 04 90 00 00 00 00,   Write Buffer: 00 A0 00 00

Type 2 PI format CDB command: 04 D0 00 00 00 00,   Write Buffer: 00 A0 00 00

9.6.3

Identifying a Protection Information drive

The Standard Inquiry 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 fur ther details with respec t to PI, please refer to SCSI Block

Commands - 3 (SBC-3) Draft Standard documentation.