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RAID running out of time?

 
 
Lawrence D'Oliveiro
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      08-05-2007
Interesting analysis <http://blogs.zdnet.com/storage/?p=162> of why, as your
disks get larger, the chance of a RAID 5 array failing will reach certainty
by about 2009, and even RAID 6 won't protect you for much longer.

The problem is that, once a drive fails and the array tries to rebuild, the
odds of hitting an unrecoverable read error (given disk sizes and current
industry-standard accepted error rates) during the rebuild will be close to
100%. And bang goes your whole array.
 
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RL
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      08-05-2007
Lawrence D'Oliveiro wrote:
> The problem is that, once a drive fails and the array tries to rebuild, the
> odds of hitting an unrecoverable read error (given disk sizes and current
> industry-standard accepted error rates) during the rebuild will be close to
> 100%. And bang goes your whole array.


RAID is not a substitute for backups, but restoring several terrabytes
may not be fun.

I am exploring using ZFS for my forhtcoming RAID deployment, because the
built-in checksums will at least give an indication of any corruption
that occurs. We can then restore from backup as appropriate.

Recently I purchased a 500GB Western Digital SATA drive (AAKS), and
managed to reliably reproduce a single-bit error by formatting the disk,
writing data to the disk, and comparing it. The error was always in the
same place within the byte. I haven't been so thorough checking the
replacement unit, but it is a worry that random data corruption can
occur so easily.

RL
 
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collector«NZ
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      08-05-2007
Lawrence D'Oliveiro wrote:
> Interesting analysis <http://blogs.zdnet.com/storage/?p=162> of why, as your
> disks get larger, the chance of a RAID 5 array failing will reach certainty
> by about 2009, and even RAID 6 won't protect you for much longer.
>
> The problem is that, once a drive fails and the array tries to rebuild, the
> odds of hitting an unrecoverable read error (given disk sizes and current
> industry-standard accepted error rates) during the rebuild will be close to
> 100%. And bang goes your whole array.


Interesting mathematics, I suppose that is why we are going to dual
system arrays with disk packs, two individual disk arrays, backing each
other up.
 
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Lawrence D'Oliveiro
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      08-09-2007
Related to the above, here's <http://blogs.zdnet.com/storage/?p=169> a post
referencing a guy's PhD thesis on the robustness of current filesystems.
They all seem to be quite poor at recovering from errors--but so what else
is new? I guess this just underlines that we have to move to something like
ZFS before too long.
 
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