Am I wrong? If not, how do I prove it short of actually setting up multiple environments for comparison?
Testing aside, if you are running an OLTP update intensive (I/O or bandwidth) environment with lots of random or sequential writes, generally speaking, even with lots of cache, avoid RAID-5 if you can -- regardless of the drive type -- if performance is absolutely crucial to you. In terms of drive preferences, again from a general standpoint, 15 K Fibre Channel (FC) and SAS drives are preferred followed by 10 K FC and SAS (or U320 SCSI) disk drives. There are some storage systems and external appliances that provide additional caching and I/O acceleration capability to mask the performance impact of RAID-5 and slower SATA disk drives.
Again, generally speaking, RAID-1 or 0+1 or 1+0 are also preferred over RAID-5 to avoid parity overhead. If your application or specific tables and objects are heavy I/O bound, then look at solid state disk (SSD), however exercise caution to make sure that you are using SDRAM and not NAND flash RAM for I/O intensive data. NAND flash is less expensive and found in hybrid disk drives or USB thumb drives. However, it is also slower than the more expensive SDRAM commonly used as cache or memory for servers.
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