SAS software benefits from the high performance of solid state drives (SSD), whether it is in the form of flash memory cards or hard-drive form-factor SSDs. The following general points should be considered when planning SSD storage for SAS usage:
• Whether in flash card or hard-drive form-factor, solid state storage is faster than traditional disk devices. Even the poorest performance we tested for SSDs (large sequential writes), solid state storage is still slightly faster than traditional storage. On the other hand, SSD is much more costly.
• Solid state storage typically performs best for random reads. The portions of SAS applications that have a lot of random components (OLAP, heavy index operations, POINT= traversals, etc.) will benefit the most.
• Random writes and sequential reads also perform far better on SSD but generally to a lesser degree than random reads. They are still much faster for typical SAS operations.
• Sequential writes on SSD storage typically exhibit a lesser degree of performance gain over traditional disk devices (in some cases, only very slightly). Garbage collection activities associated with cell-level write operations on populated disks can significantly dampen performance. The manufacturers of newer drive models may promise certain levels of improvement in speed. However, because SAS invokes so many large sequential writes, you may not realize the promised level of improvement when using SAS on these drives.
• Striping across flash cards or solid-state disks with a RAID5 stripe aggregates device performance well.
• The co-location of flash cards in system board slots and the physical distance between them affects performance.
Not all brands or device models of solid state storage are created equally, nor perform equally. Do your homework and research--sequential performance can significantly vary across models.
Many thanks to Tony Brown from SAS Performance Validation for today's content.