Disk performance, Opterons and Smartraid 5.
I wrote to the Linux Kernel Mailing List earlier this year complaining that I was getting shocking performance from a Smartraid V card, in an Opteron server, running Linux 2.6. It’s worth noting that performance seems much better if installing a 32 bit distribution and kernel is attempted.
I had a similar experience yesterday trying to recover data from an identical box, this time using the i2o_block driver rather than dpt_i2o.
At seemingly random times, the cpu would jump to 100% utilisation in io_wait, and the machine would seem to lock up as before. This happened after installing 2.6.18.1 too. After 10 minutes, the machine would spring back to life, and the cpu would be mainly idle again.
Eventually I spotted that trying to rsync some files off this computer were ‘always’ hard, and some were ‘always’ easy.
Then I noticed that the device was 52% fragmented ! It looks like this was the reason behind the bad performance. Where the slightest bit of fragmentation was present, IO performance went out of the window.
With cheap cards like the (from lspci) 0 RAID bus controller: Adaptec (formerly DPT) SmartRAID V
Controller (rev 01), and the AMD Opteron Processor 246, ext3, and linux i2o_block or dpt_i2o, the only way not to get depressing performance is to hugely overspec the space requirements on your drive, and keep an eye on how fragmented the partitions are.
Additionally, we have no problem with Adaptec AAC-RAID cards running 64 bit linux, and strongly recommend these over the i2o_block supported cards.
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