[mythtv-users] How is this pricing possible?

[Fedor Pikus]

On Wed, Mar 2, 2011 at 3:36 PM, Ajay Sharma <ajayrockrock at gmail.com> wrote:

> On Wed, Mar 2, 2011 at 12:13 PM, Alex Butcher <mythlist at assursys.co.uk>
> wrote:
> > On Wed, 2 Mar 2011, Brian Long wrote:
> >> On Tue, Feb 22, 2011 at 2:33 PM, Bobby Gill <bobbygill at rogers.com>
> wrote:
> >> I recommend you read the following post and the associated TLER posts
> before putting WD Green drives in a RAID array:
> >>
> http://shifteightgeneration.com/content/wdtler-fix-tler-setting-wd-desktop-hard-drives
> >
> > Depends on the type of RAID array one is using. TLER shouldn't really be
> a
> > big deal with Linux software (md) RAID, as if it encounters a read error,
> > it'll immediately try to read the sector from another device in the array
> > and re-write it to the device that failed (search for 'read error' in the
> md
> > manpage).  md doesn't timeout discs like some hardware controllers do:
> > <http://osdir.com/ml/linux-raid/2009-09/msg00108.html>.
>
> Thanks for this explanation.  I've been running a software raid-1
> setup for about 15 months now with green drives and haven't had any
> issues.  I figured that md was handling the lack of TLER fine but
> haven't had a chance to look it up.
>
>
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).


> --Ajay
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-- 
Fedor G Pikus (fpikus at gmail.com)
http://www.pikus.net
http://wild-light.com
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