Re: What to do about Offline_Uncorrectable and Pending_Sector in RAID1

[Wols Lists <antlists@youngman.org.uk>]

On 14/11/16 15:52, Bruce Merry wrote:
> On 13 November 2016 at 23:06, Wols Lists <antlists@youngman.org.uk> wrote:
>> > Sounds like that drive could need replacing. I'd get a new drive and do
>> > that as soon as possible - use the --replace option of mdadm - don't
>> > fail the old drive and add the new.
> Would you mind explaining why I should use --replace instead of taking
> out the suspect drive? I guess I lose redundancy for any writes that
> occur while the rebuild is happening, but I'd plan to do this with the
> filesystem unmounted so there wouldn't be any writes.

Because a replace will copy from the old drive to the new, recovering
any failures from the rest of the array. A fail-and-add will have to
rebuild the entire new array from what's left of the old, stressing the
old array much more.

Okay, in your case, it probably won't make an awful lot of difference,
but it does make you vulnerable to problems on the "good" drive. To
alter your wording slightly, you lose redundancy for writes AND READS
that occur while the array is rebuilding. It's just good practice (and I
point it out because --replace is new and not well known at present).

Cheers,
Wol