<div class="gmail_quote">On Wed, Mar 2, 2011 at 3:36 PM, Ajay Sharma <span dir="ltr"><<a href="mailto:ajayrockrock@gmail.com">ajayrockrock@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
<div class="im">On Wed, Mar 2, 2011 at 12:13 PM, Alex Butcher <<a href="mailto:mythlist@assursys.co.uk">mythlist@assursys.co.uk</a>> wrote:<br>
> On Wed, 2 Mar 2011, Brian Long wrote:<br>
>> On Tue, Feb 22, 2011 at 2:33 PM, Bobby Gill <<a href="mailto:bobbygill@rogers.com">bobbygill@rogers.com</a>> wrote:<br>
</div><div class="im">>> I recommend you read the following post and the associated TLER posts before putting WD Green drives in a RAID array:<br>
>> <a href="http://shifteightgeneration.com/content/wdtler-fix-tler-setting-wd-desktop-hard-drives" target="_blank">http://shifteightgeneration.com/content/wdtler-fix-tler-setting-wd-desktop-hard-drives</a><br>
><br>
> Depends on the type of RAID array one is using. TLER shouldn't really be a<br>
> big deal with Linux software (md) RAID, as if it encounters a read error,<br>
> it'll immediately try to read the sector from another device in the array<br>
> and re-write it to the device that failed (search for 'read error' in the md<br>
> manpage). md doesn't timeout discs like some hardware controllers do:<br>
> <<a href="http://osdir.com/ml/linux-raid/2009-09/msg00108.html" target="_blank">http://osdir.com/ml/linux-raid/2009-09/msg00108.html</a>>.<br>
<br>
</div>Thanks for this explanation. I've been running a software raid-1<br>
setup for about 15 months now with green drives and haven't had any<br>
issues. I figured that md was handling the lack of TLER fine but<br>
haven't had a chance to look it up.<br>
<font color="#888888"><br></font></blockquote><div><br>I don't think it's really an issue for RAID-1, if one disk has a glitch md will just try to update it from the other one, so you will see a resync. md will periodically resync the array anyway (at least it does that in recent versions, my Centos5 boxes all do it), so every now and then you can catch resyncs in /proc/mdstat. Once I had a SATA error, the disk did not drop out but md reconstructed the mirror. Since RAID-1 is a simple mirror, with each disk holding a valid filesystem, nothing will go wrong unless both disks suffer hard (not intermittent) failure in a short time. The problem with RAID-5 is that if a resync is triggered and then another disk has an intermittent failure during read, now md cannot resync the array. If you have a 2TB disk, the chances of a single read error during the read of the whole 2TB are pretty high (some estimates put it close to 100%). I've seen recommendations to use RAID-1 or RAID-6 with large disks, instead of RAID-5 (I've done that with my main server, 6 1.5TB disks).<br>
</div><blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;"><font color="#888888">
--Ajay<br>
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