Solid State Disks

Some controllers and drive trays now support Solid State Disks (SSDs). SSDs are data storage devices that use solid state memory (flash) to store data persistently. An SSD emulates a conventional hard drive, thus easily replacing it in any application. SSDs are available with the same interfaces used by hard drives: Serial Attached SCSI (SAS), Serial Advanced Technology Attachment (SATA), and Fibre Channel (FC).

The advantages of SSDs over hard drives are:

SSD support is a premium feature of the storage management software that must be enabled by either you or your storage vendor.

Identifying SSDs

You can identify SSDs in the storage management software either by the label “SSD” or this icon:

In addition to drive firmware, SSDs have field-programmable gate array (FPGA) code that might be updated periodically. An FPGA version is listed in the drive properties, which you can see in the storage management software by selecting a drive on the Physical tab. Also, SSDs do not have a speed listed in the drive properties like hard drives do.

Creating Volume Groups

All of the drives in a volume group must have the same media type (hard drive or SSD) and the same interface type (FC, SAS, or SATA). Hot spare drives must also be of the same drive type as the drives they are protecting.

Wear Life

A flash-based SSD has a limited wear life before individual memory locations can no longer reliably persist data. The drive continuously monitors itself and reports its wear life status to the controller. Two mechanisms exist to alert you that an SSD is nearing the end of its useful life: average erase count and spare blocks remaining. You can find these two pieces of information in the drive properties, which you can see in the storage management software by selecting a drive on the Physical tab.

The average erase count is reported as a percentage of the rated lifetime. When the average erase count reaches 80 percent, an informational event is logged to the Major Event Log (MEL). At this time, you should schedule the replacement of the SSD. When the average erase count reaches 90 percent, a critical event is logged, and a Needs Attention condition occurs. At this time, you should replace the SSD as soon as possible.

The spare blocks remaining are reported as a percentage of the total blocks. When the spare blocks remaining falls below 20 percent, an informational event is logged to the MEL. At this time, you should schedule the replacement of the SSD. When the spare blocks remaining falls below 10 percent, a critical event is logged, and a Needs Attention condition occurs. At this time, you should replace the SSD as soon as possible.

Write Caching

Write caching will always be enabled for SSDs. Write caching improves performance and extends the life of the SSD.

Background Media Scans

You cannot enable background media scans on SSDs. Background media scans are not needed for SSDs because of the high reliability of SSDs. Furthermore, background media scans would be detrimental because they increase wear on the SSDs.

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