[Lustre-discuss] software raid

[Cliff White]

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 <sdm900 at gmail.com> 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
> sdm900 at gmail.com
>
>
>
> 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: briano at sgi.com, 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
> > -----------------------------------------------------------------------
> >
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>
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-- 
cliffw
Support Guy
WhamCloud, Inc.
www.whamcloud.com
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