HP ML350 Drive technology overview - Page 10

HP solid state drive reliability requirements - proliant memory

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advances in flash memory as well as the rapidly evolving capabilities of NAND flash memory controllers, HP has been able to develop solid state drives that can meet the performance and reliability requirements for use in server environments. Figure 1. HP second generation solid state drive. Note: Shipping product may differ slightly in appearance HP solid state drive reliability requirements As with traditional disk drives, all SSDs are not the same. HP engineering has applied a great deal of effort to ensure that HP server SSDs can meet the reliability and endurance requirements of server storage. HP SSDs use several different technologies and design requirements to achieve this goal. NAND over provisioning and wear-levelling Unlike spinning media, NAND memory has a well defined lifespan. This lifespan is based on the number of write/erase cycles performed. In order to meet the endurance requirements for server environments, HP SSDs make extensive use of both wear-leveling and NAND over provisioning. Wear-leveling uses sophisticated algorithms to continuously re-map logical SCSI blocks that are being frequently written to different physical pages in the NAND array. Wear leveling ensures that erasures and rewrites remain evenly distributed across the medium, maximizing the endurance of the SSD. This logical-to-physical map is maintained as a pointer array in high speed DRAM on the SSD controller. It is also maintained algorithmically in metadata regions in the NAND flash array itself. This ensures that the map can be re-built in the case of an unexpected power loss. HP also ensures the endurance of SSDs by over-provisioning the amount of NAND capacity on the device. On higher end SSDs, NAND can be over-provisioned by as much as 25 percent above the stated storage capacity. Over-provisioning increases the endurance of an SSD by distributing the total number of writes and erases across a larger population of NAND blocks and pages over time. Power loss protection The controllers in SSDs use pointer arrays and other structures to maintain the data required for SSD operation, including the SCSI logical block-to-NAND page mapping and other information. In order to increase overall performance, this data is kept in high speed DRAM on the controller and periodically written to metadata regions in the NAND flash array itself. All HP ProLiant SSDs feature power loss protection, which ensures that in the case of power loss to the drive (including hot plug removal) all of this information is written to the NAND metadata. SSDs with power loss protection can 10

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advances in flash memory as well as the rapidly evolving capabilities of NAND flash memory
controllers, HP has been able to develop solid state drives that can meet the performance and
reliability requirements for use in server environments.
Figure 1. HP second generation solid state drive.
Note: Shipping product may differ slightly in appearance
HP solid state drive reliability requirements
As with traditional disk drives, all SSDs are not the same. HP engineering has applied a great deal of
effort to ensure that HP server SSDs can meet the reliability and endurance requirements of server
storage. HP SSDs use several different technologies and design requirements to achieve this goal.
NAND over provisioning and wear-levelling
Unlike spinning media, NAND memory has a well defined lifespan. This lifespan is based on the
number of write/erase cycles performed. In order to meet the endurance requirements for server
environments, HP SSDs make extensive use of both wear-leveling and NAND over provisioning.
Wear-leveling uses sophisticated algorithms to continuously re-map logical SCSI blocks that are being
frequently written to different physical pages in the NAND array. Wear leveling ensures that erasures
and rewrites remain evenly distributed across the medium, maximizing the endurance of the SSD. This
logical-to-physical map is maintained as a pointer array in high speed DRAM on the SSD controller. It
is also maintained algorithmically in metadata regions in the NAND flash array itself. This ensures
that the map can be re-built in the case of an unexpected power loss.
HP also ensures the endurance of SSDs by over-provisioning the amount of NAND capacity on the
device. On higher end SSDs, NAND can be over-provisioned by as much as 25 percent above the
stated storage capacity. Over-provisioning increases the endurance of an SSD by distributing the total
number of writes and erases across a larger population of NAND blocks and pages over time.
Power loss protection
The controllers in SSDs use pointer arrays and other structures to maintain the data required for SSD
operation, including the SCSI logical block-to-NAND page mapping and other information. In order
to increase overall performance, this data is kept in high speed DRAM on the controller and
periodically written to metadata regions in the NAND flash array itself. All HP ProLiant SSDs feature
power loss protection, which ensures that in the case of power loss to the drive (including hot plug
removal) all of this information is written to the NAND metadata. SSDs with power loss protection can