Historically, Linux software RAID had multiple issues, we did not advise using it. Those issues afaik were fixed long ago, and we changed the advice. Sun/Oracle sold a product that was based on software RAID - there are no unique issues using soft RAID with Lustre.
Performance/reliability is a whole 'nother set of topics - there are reasons why people buy the expensive flavors., cliffw On Thu, Mar 24, 2011 at 3:34 AM, Stuart Midgley <[email protected]> wrote: > Hi Brian > > Long time no speak. > > Anyway, we use to use software raid exclusively but have slowly stopped. > Using 3ware cards in Rackable nodes now. All going well so far. Though, > for our MDS we are running a 3 way mirror on sas disks. > > md has a few issues... all of them tend to end at the same place... losing > data. We have had situations where md returns crap data cause its getting > it from a disk, but doesn't actually verify it against other disks (the disk > hasn't actually thrown hardware errors)... you manually fail the disk and > all of a sudden the file is no longer corrupt. > > We have also had situations where md says the write occurred successfully, > but really it has just hit the cache on the disk and hasn't been committed > to platter... and a short time later, the disk reports the error to md but > for a much earlier read/write. The data is now corrupt on disk and flushed > form all of lustre's caches. > > With all our software raid we now do /sbin/hdparm -W 0 "$dev" to disable > write caching on the disk. This has helped, but obviously hurts > performance. > > > > > > -- > Dr Stuart Midgley > [email protected] > > > > On 24/03/2011, at 10:54 AM, Brian O'Connor wrote: > > > > > This has probably been asked and answered. > > > > Is software raid(md) still considered bad practice? > > > > I would like to use ssd drives for an mdt, but using fast ssd drives > > behind a raid controller seems to defeat the purpose. > > > > There was some thought that the decision not to support > > software raid was mostly about Sun/Oracle trying to sell hardware > > raid. > > > > thoughts? > > > > -- > > Brian O'Connor > > ----------------------------------------------------------------------- > > SGI Consulting > > Email: [email protected], Mobile +61 417 746 452 > > Phone: +61 3 9963 1900, Fax: +61 3 9963 1902 > > 357 Camberwell Road, Camberwell, Victoria, 3124 > > AUSTRALIA > > http://www.sgi.com/support/services > > ----------------------------------------------------------------------- > > > > _______________________________________________ > > Lustre-discuss mailing list > > [email protected] > > http://lists.lustre.org/mailman/listinfo/lustre-discuss > > _______________________________________________ > Lustre-discuss mailing list > [email protected] > http://lists.lustre.org/mailman/listinfo/lustre-discuss > -- cliffw Support Guy WhamCloud, Inc. www.whamcloud.com
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