Mailinglist Archive: opensuse (1962 mails)

["Greg Freemyer" <greg.freemyer@xxxxxxxxx>]

On Wed, Nov 12, 2008 at 11:01 AM, Greg Freemyer <greg.freemyer@xxxxxxxxx> wrote:
> On Wed, Nov 12, 2008 at 6:08 AM, Sandy Drobic
> <suse-linux-e@xxxxxxxxxxxxxxxxxxxxxxx> wrote:
> > Per Jessen wrote:
> Not necessarily.  Drives only remap bad sectors on write.  So if you
> have sectors you only read that go bad, they will never be repaired by
> the hard drive itself.
>
> There has been discussion that linux software raid should scan an
> array in the background and when it finds a media error, recreate the
> data from the rest of the array, then write the known good data back
> to the bad sector, thus triggering the remapping logic of the drive
> itself.
>
> I don't know if this is part of current generation kernels or not.
> Possibly it was just talk.

I asked on the mdraid list.

With linux software raid, any time a media error is experienced and
the data can be recreated from other drives, the original failed
sector is re-written with the assumption it will trigger a re-mapping
event.  That was implemented around 2.6.16.

So that is great, but the kernel does NOT proactively scan the drives
looking for bad media sectors thus a rarely read sector could go bad
and stay that way for an extended time.

Apparently you can implement a background scan via mdadm and invoke
that from cron as desired.  I my opinion I make that a best practice.
I have always used 3ware based arrays in the past, but my
investigations into mdraid have been so positive I am likely to switch
for the future.

HTH
Greg
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