[ale] disk drive diagnostics nirvana - NOT - I have questions

[Derek Atkins]

Phil Turmel <philip at turmel.org> writes:

> My critical servers all use linux software raid in various combinations,
> and all of the raid arrays are scrubbed weekly.  By scrubbed, I mean a
> cron job instructs the kernel to read every sector on every member
> device in the background, compute parity as appropriate, and report any
> inconsistencies.  Any read errors trigger the corresponding recovery and
> rewrite functions that would normally occur if an application
> encountered the sectors.  Any unsuccessful write kicks that device out
> of the array as usual.

I thought that the raid scrub did a read/write of every sector, not just
a read?

> I have been doing this for about ten years now, with about seven or
> eight drive failures in that time.  Never lost any data, though I've
> been nervous a few times when waiting for a replacement disk for a raid5
> array.  Everything is now raid6 or triple-mirrored, so I sleep well.

I use RAID-10 personally.

> All of the drives that failed on me had fewer than 100 relocated
> sectors.  None of them had fewer than 20 relocated sectors.  Mostly
> 30,000+ hours of operation.  This seems to correspond well to the
> reports I read on the linux-raid mailing list.  I tolerate drives with
> single-digit relocation counts, but I recheck them every week.  After
> that, they're outa there.

Agreed.

> Some of the research on the topic suggests that climbing relocation
> counts is most often caused by approaching spindle bearing failure,
> where the wobble causes head tracking errors.  Whatever the underlying
> reason, that's my red line.

I look for a new drive as soon as I get the first errors (assuming I
don't happen to have a cold spare on hand).

> HTH,
>
> Phil

-derek

-- 
       Derek Atkins, SB '93 MIT EE, SM '95 MIT Media Laboratory
       Member, MIT Student Information Processing Board  (SIPB)
       URL: http://web.mit.edu/warlord/    PP-ASEL-IA     N1NWH
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