Historically, Linux software RAID had multiple issues, we did not advise using it.<br>Those issues afaik were fixed long ago, and we changed the advice.<div>Sun/Oracle sold a product that was based on software RAID - there are no unique issues</div>
<div>using soft RAID with Lustre.</div><div><br></div><div>Performance/reliability is a whole 'nother set of topics - there are reasons why people</div><div>buy the expensive flavors.,</div><div>cliffw<br><br><div class="gmail_quote">
On Thu, Mar 24, 2011 at 3:34 AM, Stuart Midgley <span dir="ltr"><<a href="mailto:sdm900@gmail.com">sdm900@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
Hi Brian<br>
<br>
Long time no speak.<br>
<br>
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.<br>
<br>
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.<br>
<br>
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.<br>
<br>
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.<br>
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<br>
<br>
<br>
--<br>
Dr Stuart Midgley<br>
<a href="mailto:sdm900@gmail.com">sdm900@gmail.com</a><br>
</font><div><div></div><div class="h5"><br>
<br>
<br>
On 24/03/2011, at 10:54 AM, Brian O'Connor wrote:<br>
<br>
><br>
> This has probably been asked and answered.<br>
><br>
> Is software raid(md) still considered bad practice?<br>
><br>
> I would like to use ssd drives for an mdt, but using fast ssd drives<br>
> behind a raid controller seems to defeat the purpose.<br>
><br>
> There was some thought that the decision not to support<br>
> software raid was mostly about Sun/Oracle trying to sell hardware<br>
> raid.<br>
><br>
> thoughts?<br>
><br>
> --<br>
> Brian O'Connor<br>
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</div></div></blockquote></div><br><br clear="all"><br>-- <br>cliffw<div>Support Guy</div><div>WhamCloud, Inc.</div><div><a href="http://www.whamcloud.com" target="_blank">www.whamcloud.com</a></div><div><br></div><br>
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