Messages in this thread | | | Date | Mon, 03 Jun 2002 09:35:30 +0200 | From | Kasper Dupont <> | Subject | Re: RAID-6 support in kernel? |
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Roy Sigurd Karlsbakk wrote: > > hi all > > I'n working on server setup with some 16 disks in RAID-5; one of them a > spare. After a little reading, I find myself longing for support for > RAID-6 support in kernel, giving the opportunity to allow for two failed > drives without a chrash (see links about RAID-6 below if interested). > > I am aware of that not all kernel hackers like such configurations, and > that some will rather see small RAID-configurations connected with VLM. > I beleive there is a reason for using RAID-6, and RAID-controller vendors > (such as Compaq) are already using them, so why shouldn't linux do so > also? With a high number of cheap IDE drives, the chance of one failing is > quite high, so why not RAID-6? At least for a system doing most reads... > > thanks > > roy > > RAID-6 layout: http://www.acnc.com/04_01_06.html
If it is supposed to survive two arbitrary disk failures something is wrong with that figure. They store 12 logical sectors in 20 physical sectors across 4 drives. With two lost disks there are 10 physical sectors left from which we want to reconstruct 12 logical sectors. That is impossible.
OTOH it is possible to construct a system with optimal capacity and ability to survive any chosen number of disk failures. This can be done using either a Reed-Soloman code or Lagrange interpolation of polynomials over a finite field.
However I guess those techniques would be inefficient in software.
-- Kasper Dupont -- der bruger for meget tid på usenet. For sending spam use mailto:razor-report@daimi.au.dk - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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