On Tue, Oct 13, 2009 at 02:56:17PM -0700, Michael Evans wrote: > If you're only using 4 drives, Raid 10 (linux has a raid level that operates > this way natively, but reshaping was not-yet supported when I last > checked.)(or raid 0 across multiple raid 1 block devices) would yield > superior performance across every dimension except fault tolerance. That is > the one advantage raid6 would have with that few devices, any 2 could fail > and data would still be intact; while with the raid solution the right two > drives failing could corrupt/destroy half the data. > > Raid6 makes more sense with large quantities of devices (at least 6 IMO) > when latency isn't as much of an issue as bandwidth. In particular > Databases and small file serving operations probably operate better off of > raid10/1+0; while most operations on large files would benefit more from the > raid 0 (across N-redundancy) devices performance of raid 5/6 for the typical > case of fault free operations.
I understand this will be a bit of a religious issue, so I'll just start out by stating things in a ridiculously dismissive tone: Do not use RAID5 or RAID6 for anything at all. Ever. For any reason. * The alternative, RAID1 or RAID10, is negligably more expensive, even for home use. * RAID5/6 is slower, especially on writes. * The larger the drive, the more likely that rebuilds will fail. My own recent experience with >1TB drives has been that a 4-drive array will rebuild itself into something usable a bit less than half the time. * Rebuilds will silently spread any data corruption across all drives in the array (and the chances of such small amounts of silent data corruption are high, and increasing). Reference: http://baarf.com -- Robert Woodcock - [email protected] perl -e '$a-=($_%4-2)*4/$_++while++$_<2e6;print"$a\n"'
