lkml.org 
[lkml]   [2002]   [Jun]   [3]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: RAID-6 support in kernel?
    On Mon, Jun 03, 2002 at 02:25:22AM -0700, Derek Vadala wrote:
    > On Mon, 3 Jun 2002, Roy Sigurd Karlsbakk wrote:
    >
    > > It'll waste 9 drives, giving me a total capacity of 7n instead of 14n.
    > > And, by definition, RAID-6 _can_ withstand _any_ two-drive failure.
    >
    > This is certainly not true.
    >
    > Combining N RAID-5 into a stripe wastes on N disks.
    >
    > If you combine two it wastes 2 disks, etc.
    >
    > That is, for each RAID-5 you waste a single disk worth of storage for
    > partiy. I don't know what equation you're using where you get 9 drives
    > from.

    He was thinking "mirror", not "stripe". Mirror of 2 RAID-5 arrays (would
    be probably called RAID-15 (when there is a RAID-10 for mirrored stripe
    arrays)), can withstand any two disks failing anytime. Even more for
    certain combinations. But it is terribly inefficient.

    > As far as it's ability to withstand _any_ 2-disk failure... I'm not sure
    > what you mean by definition. RAID-6 implemations don't follow a standard
    > because there isn't one. Depending on how it's implemented, RAID-6 is not
    > necessarily able to withstand a filaure of any two disks. We can argue as
    > much as you want, but I'm not willing to invest the time.
    >
    > > With a 1500MHz Athlon on a typical file server where there's not much
    > > writes, the CPU is sitting there chrunching RC5-64 som 99,95 % of the
    > > time. I don't think it'll make much differnce with today's CPUs
    >
    > It's up to you to decide if the performance trade-off is worthwhile. I
    > merely trying to point out that system with 2 RAID-5 is likely to incur
    > the same CPU hit as a single RAID-6, implemented in the kernel.

    --
    Vojtech Pavlik
    SuSE Labs
    -
    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/

    \
     
     \ /
      Last update: 2005-03-22 13:26    [W:2.463 / U:0.004 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site