Giovanni Tessore wrote:
I have never seen a properly good disk that gets that high of error
rate actually exposed to the OS. I have dealt with >5000 disk for
several years of history on the 5000+ disks.
I have experience with not so many disks, but I was used that they are
quite reliable, and that the first read error reported to OS is symptom
of an incominc failure; I always replaced them in such case, and this is
why I am so amazed that kernel 2.6.15 changed the way it manages read
errors (as also Asdo said, it's ok for raid-6, but unsafe for raid-5, 1,
4, 10).
Good disks to rescan, and replace the bad blocks before you see them,
if you help the disks by doing your own scan then things are better.
Actually I had not a single read error since 2-3 years on my systems,
but now ... in a week, I had 4 disk failed (yes... another one since I
started this thread!!) ... it's 30% of the total disks in my systems ...
so I'm really puzzled out ... I don't know what to trust ... I'm just in
the hands of God
That tells me you have one of those "bad" lots. If the disks start
failing in mass in <3-4 years it is usually a bad lot. You can
manually scan (read) the whole disk, and if the sectors take weeks to
go bad then the normal disk reallocation will prevent errors (if you
are scanning faster than they go fully bad--the disk will replace when
the error rate is high, but not so high that the disk can internally
reconstruct the data). The more often that you scan, the higher rate
of sectors going bad can be corrected.
The reason that md rewrites and does not knock out the read errors, is
when you get a read error you do not know if you can read the other
disks. Consider that if you have 5 crappy disks that have say 1000
read errors per disk, the chance of one of the other of disks having
the same sector bad is fairly small. But given that one disk has a
read error, the odds of another disk also having a read error is alot
more likely, especially if none of the other disks have been read in
several months.
What kind of disks are they? And were you doing checks on the arrays
and if so how often? If you never do checks then a sector won't get
check and moved before it goes fully bad, and can have months of not
being read to go completely bad.
Nothing in the error rate indicated that behavior, so if you get a bad
lot it will be very bad, if you don't get a bad lot you very likely
won't have issues. Now including the bad lots data into the overall
error rate, may result in the error rate being that high, but you luck
will depend on if you have a good or bad lot.
My disks are form same manufacturer as size, but different lot, as
bought in different times, and different models.
Systems are well protected by UPS and in different places!
... my unluky week .. or I have a big EM storm over here...
I've recall to duty old 120G disks to save some data.
The same manufacturer process usually extends over different sizes
(same underlying platter density), and over several months. The last
time I saw the issue 160gb, and 250 gb enterprise and non-enterprise
disks will all affected. The symptom was that the sectors went bad
really really fast, I would suspect that there was a process issues
with either the design, manufacturer, or quality control of the
platter that resulting in the platters going bad at a much higher rate
than expected.
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