On Sun, Feb 5, 2012 at 5:31 PM, Ross Walker <rswwalker at gmail.com> wrote: > On Feb 5, 2012, at 10:32 AM, Phil Schaffner <Philip.R.Schaffner at NASA.gov> > wrote: > > > Boris Epstein wrote on 02/04/2012 11:57 AM: > >> What is RAID0+1? > > > > Nested RAID. Paraphrasing http://en.wikipedia.org/wiki/RAID : > > > > For a RAID 0+1, drives are first combined into multiple level 0 RAIDs > > that are themselves treated as single drives to be combined into a > > single RAID 1. > > Probably the worse setup, a failure on both sides of a mirror means total > loss and with the # of disks on each side of this setup the chance of this > is much greater, recovery from a failure is a lot longer cause the whole > stripe needs to re-mirror. While performance of reads is equal to 1+0 the > writes are equal to a single mirror cause both sides need to complete > before the next operation can run or only one write operation on the array > at a time. > > Much better RAID level is 1+0 which is a series of mirrors striped > together. While a failure on both sides of any one mirror is total for the > array there is only 1 disk on either side so the odds are less, recovery > from failure is faster as well cause only one disk needs to be re-mirrored. > Performance of reads and writes are equal because each mirror can perform > writes independant of the others, or # of write operations equal to the > number of mirrors. > > -Ross > > _______________________________________________ > CentOS mailing list > CentOS at centos.org > http://lists.centos.org/mailman/listinfo/centos > Ross, What you are saying seems to make sense actually. I wonder how much a RAID6 with a few spares would make sense. If we are talking a large number of disks then RAID 6 + 2 spares means overpaying only for 5 disks. Not a lot if the total number of them is, say, 20. Boris.