10.4Background Media Scan

Background Media Scan (BMS) is a self-initiated media scan. BMS is defined in the T10 document SPC-4 available from the T10 committee. BMS performs sequential reads across the entire pack of the media while the drive is idle. In RAID arrays, BMS allows hot spare drives to be scanned for defects prior to being put into service by the host system. On regular duty drives, if the host system makes use of the BMS Log Page, it can avoid placing data in suspect locations on the media. Unreadable and recovered error sites will be logged or reallocated per ARRE/AWRE settings.

With BMS, the host system can consume less power and system overhead by only checking BMS status and results rather than tying up the bus and consuming power in the process of host-initiated media scanning activ- ity.

Since the background scan functions are only done during idle periods, BMS causes a negligible impact to sys- tem performance. The first BMS scan for a newly manufactured drive is performed as quickly as possible to verify the media and protect data by setting the “Start time after idle” to 5ms, all subsequent scans begin after 500ms of idle time. Other features that normally use idle time to function will function normally because BMS functions for bursts of 800ms and then suspends activity for 100ms to allow other background functions to operate.

BMS interrupts immediately to service host commands from the interface bus while performing reads. BMS will complete any BMS-initiated error recovery prior to returning to service host-initiated commands. Overhead associated with a return to host-servicing activity from BMS only impacts the first command that interrupted BMS, this results in a typical delay of about 1 ms.

10.5Media Pre-Scan

Media Pre-Scan is a feature that allows the drive to repair media errors that would otherwise have been found by the host system during critical data accesses early in the drive’s life. The default setting for Media Pre-Scan is enabled on standard products. Media Pre-Scan checks each write command to determine if the destination LBAs have been scanned by BMS. If the LBAs have been verified, the drive proceeds with the normal write command. If the LBAs have not been verified by BMS, Pre-Scan will convert the write to a write verify to certify that the data was properly written to the disc.

Note. During Pre-Scan write verify commands, write performance may decrease by 50% until Pre-Scan completes. Write performance testing should be performed after Pre-Scan is complete. This may be checked by reading the BMS status.

To expedite the scan of the full pack and subsequently exit from the Pre-Scan period, BMS will begin scanning immediately when the drive goes to idle during the Pre-Scan period. In the event that the drive is in a high transaction traffic environment and is unable to complete a BMS scan within 24 power on hours BMS will dis- able Pre-Scan to restore full performance to the system.

10.6Deferred 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 oper- ations performed by the drive. When a write command is received for an LBA marked for DAR, the auto-reallo- cation 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 unread- able 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.

48

Constellation ES Series SAS Product Manual, Rev. E

Page 55 Page 57
Page 56
Image 56
Seagate ST31000426SS, ST31000425SS, ST31000424SS manual Background Media Scan, Media Pre-Scan, Deferred Auto-Reallocation
Page 55 Page 57

ST3500414SS, ST3500415SS, ST32000445SS, ST31000425SS, ST32000446SS specifications

Seagate, a leader in data storage solutions, has introduced a range of high-capacity and reliable hard drives designed for enterprise environments, including the Seagate ST31000424SS, ST3500416SS, ST31000426SS, ST32000444SS, and ST32000446SS. Each of these models is built with an emphasis on performance, endurance, and advanced data protection technologies, catering to mission-critical applications and data-intensive workloads.

The ST31000424SS is a 1TB drive designed for servers and data centers. It offers a 7,200 RPM spindle speed and a 6 Gb/s SATA interface, ensuring quick data access and transfer rates. With a 64MB cache buffer, the ST31000424SS provides enhanced read/write performance, making it suitable for applications that demand quick responses from the storage subsystem.

Similarly, the ST3500416SS is a high-capacity 500GB model, also spinning at 7,200 RPM with a 6 Gb/s SATA interface. This drive is ideal for mid-range servers and enterprise storage, providing an excellent balance of performance and capacity for users looking to optimize their storage efficiency while maintaining lower power consumption.

The ST31000426SS expands the capacity to 1TB while retaining the same reliability and performance characteristics as its counterparts. Its robust design ensures reliability in multi-drive environments, making it an appealing choice for virtualization and database applications, where performance is critical.

The ST32000444SS and ST32000446SS represent Seagate's commitment to higher capacities, with both offering 2TB of storage. They both feature 7,200 RPM speeds, 6 Gb/s SATA interfaces, and 64MB cache buffers, catering to high-demand environments such as cloud storage and data analytics. The drives also integrate advanced error recovery and data integrity features, ensuring the protection of sensitive data, which is vital for enterprise users.

Each model supports Seagate's PowerChoice technology, which optimizes power consumption without sacrificing performance, enhancing energy efficiency in modern data centers. With a broad range of capacities and performance levels, these Seagate drives provide scalable solutions tailored to meet the robust demands of today’s enterprise applications, ensuring reliability and performance for critical data operations.
Top Page Image Contents