9.6DEFERRED AUTO-REALLOCATION

Deferred Auto-Reallocation (DAR) simplifies reallocation algorithms at the system level by allowing the drive to reallocate unreadable locations on a subsequent write command. Sites are marked for DAR during read operations performed by the drive. When a write command is received for an LBA marked for DAR, the auto-reallocation process is invoked and attempts to rewrite the data to the original location. If a verification of this rewrite fails, the sector is re-mapped to a spare location.

This is in contrast to the system having to use the Reassign Command to reassign a location that was unreadable and then generate a write command to rewrite the data. DAR is most effective when AWRE and ARRE are enabled—this is the default setting from the Seagate factory. With AWRE and ARRE disabled DAR is unable to reallocate the failing location and will report an error sense code indicating that a write command is being attempted to a previously failing location.

9.7IDLE READ AFTER WRITE

Idle Read After Write (IRAW) utilizes idle time to verify the integrity of recently written data. During idle periods, no active system requests, the drive reads recently written data from the media and compares it to valid write command data resident in the drives data buffer. Any sectors that fail the comparison result in the invocation of a rewrite and auto-reallocation process. The process attempts to rewrite the data to the original location. If a verification of this rewrite fails, the sector is re-mapped to a spare location.

9.8PROTECTION 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.

9.8.1Levels 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 (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.

9.8.2Setting 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

9.8.3Identifying 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 further details with respect to PI, please refer to SCSI Block Commands - 3 (SBC-3) Draft Standard documentation.

CONSTELLATION ES.1 SAS PRODUCT MANUAL, REV. G

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Seagate ST2000NM0063 manual Levels of PI, Setting and determining the current Type Level
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ST2000NM0063 specifications

The Seagate ST2000NM0063 is a high-performance internal hard disk drive designed for enterprise environments, offering a robust solution for those requiring reliable data storage. With a storage capacity of 2TB, this drive is ideal for both small and large enterprises, catering to applications ranging from data centers to surveillance systems.

One of the main features of the ST2000NM0063 is its 7200 RPM rotational speed, which ensures rapid data access and improved overall performance. This speed allows for faster read and write times, making it suitable for applications that demand quick data retrieval and processing. The drive supports a SATA 6Gb/s interface, which provides enhanced data transfer rates. This modern interface is essential for maximizing throughput, particularly when deployed in environments where speed is critical.

In terms of technology, the Seagate ST2000NM0063 utilizes Advanced Format Technology, enhancing data storage efficiency and increasing the number of user-addressable sectors. This feature allows for better alignment of data on the drive, which can lead to improved performance and reliability. Additionally, the drive incorporates the Seagate PowerChoice technology, enabling energy-efficient operations. This technology helps reduce power consumption during idle periods, contributing to lower operating costs and a smaller carbon footprint.

The ST2000NM0063 also emphasizes data integrity and reliability. Equipped with features such as error recovery control and vibration tolerance, this drive is designed to operate in challenging conditions. These attributes make it an excellent choice for RAID configurations and other enterprise applications that require high data availability and protection against data loss.

Furthermore, the ST2000NM0063 has a mean time between failures (MTBF) rating of 1.2 million hours, signifying its durability and long lifespan. This reliability is crucial for critical business applications where downtime is not an option.

In summary, the Seagate ST2000NM0063 combines high capacity, excellent performance, and advanced technologies to meet the demanding needs of enterprise storage. Its reliability, efficiency, and robust features make it a preferred choice for organizations looking to enhance their data storage solutions while ensuring optimal performance and longevity. Whether utilized in cloud storage, surveillance, or data center applications, this hard drive stands out as a dependable component in any IT infrastructure.
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