Re: 5.1 to 5.5 upgrade causes significant write slowdown (MyISAM + indexes)

[Rick James]

Sorry, I can't advise on specific hardware.

RAID striping (0,5,6,10) is beneficial for heavy writes (single or multiple threads) and for multiple threads doing heavy reading. The number of I/Os per second is doubled or tripled (etc), depending on the config.

RAID with BBWC (Battery Backed Write Cache) makes writes "instantaneous", while being safe from power failures. A brief burst of writes takes no time; a lot of writes would eventually overwhelm the cache at which point writes would slow to disk speed. (Striping helps.)

RAID with mirroring or parity (1,5,6,10) protects you from a single (sometimes multiple) disk failures. The server might even be designed to let you replace a dead drive out without shutting down the system.

So, for serious, big, usage: Hardware RAID with BBWC -5 or -10. RAID-5 gives you more disk space; RAID-10 (or -6?) gives you more protection from drive failures.

If you want to cut corners ($$$), I have given you some of the tradeoffs. The Wikipedia page is excellent for more details.