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List:       linux-raid
Subject:    Re: want_replacement (aka --replace)
From:       Piergiorgio Sartor <piergiorgio.sartor () nexgo ! de>
Date:       2013-04-27 7:04:59
Message-ID: 20130427070459.GA2246 () lazy ! lzy
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Hi Keith,

On Fri, Apr 26, 2013 at 08:18:40PM -0700, Keith Keller wrote:
> Hi all,
> 
> For other reasons I moved one of my md servers to kernel 3.8, and on a
> whim I decided to test --replace on a RAID6 array.  For this test I used
> mdadm from Neil's git repository, but from a read of the md kernel
> documentation you could probably do this just from manipulating
> /sys/block/mdN/md/ appropriately if you don't or can't get the latest
> mdadm.
> 
> It went very smoothly in my test.  I marked one drive with --replace,
> and the array started rebuilding with the new drive, without any IO from
> the other members of the array.  It took much less time than a full
> rebuild, and when it was done, the old drive was marked faulty, as
> expected.
> 
> This is really an amazing feature!  I can see at least two use cases for
> it:
> 
> ==you suspect a drive is failing but it hasn't been kicked yet
> ==you want to replace all the drives with larger drives in order to grow
> the array
> 
> Are there any other use cases?  In the scenario where the drive marked

my further idea would be to "rotate" a spare,
so that the different HDDs will have, in the
end, different power on hours.
Of course, the spare must be idle while not
in use.

bye,

pg

> as wanting replacement fails completely, does md fall back to a full
> rebuild with the new drive?  Can it pick up in the middle or does it
> have to start over?
> 
> Thanks to Neil and the other md developers for such a great feature.
> 
> --keith
> 
> -- 
> kkeller@wombat.san-francisco.ca.us
> 
> 
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-- 

piergiorgio
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