On Mon, 4 Jun 2007, Rafael Ferreira wrote:
Can I ask why use a hardware controller instead of a MD device? MD devices are tons more capable and you wouldn't have problems with drivers. Also, from my experience, performance differences between hardware and software RAID are so small (unless you are in a CPU limited embedded environment) that are only noticeable in synthetic benchmarks and will never be noticeable in real life scenarios.
Now, I am a total elitist about this sort of thing; all my disks are SCSI/Fibre-channel - if it's not 10KRPM I don't use it for anything but backups. I also don't use anything but raid 0, 1 or 0+1. really, this is the best-case scenario for software raid, as there's lots of neat stuff a hw raid controller can do to speed up raid5 (raid5 still sucks, though, at least for any application that requires modifying data or any application that requires decent performance during single disk down/rebuild.)
Anyhow, the performance of md has been great. the problem has been reliability; several times things have frozen up hard with a read or write error to one of the disks in a mirror. after a reboot, everything was fine, but it still screws my SLA. I've never seen this with a hardware raid card; H/W raid cards tend to fail the disk and move on. (any reccomendations on fibre h/w raid? something cheap on ebay?)
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