Bob Friesenhahn wrote:
On Tue, 28 Apr 2009, Richard Elling wrote:
Yes and there is a very important point here.
There are 2 different sorts of scrubbing: read and rewrite.
ZFS (today) does read scrubbing, which does not reset the decay
process. Some RAID arrays also do rewrite scrubs which does reset
the decay process. The problem with rewrite scrubbing is that you
I am not convinced that there is a "decay" process. There is
considerable magnetic hysteresis involved. It seems most likely that
corruption happens all of a sudden, and involves more than one or two
bits. More often than not we hear of a number of sectors failing at
one time.
I suppose if you could freeze the media to 0K, then it would not decay.
But that isn't the world I live in :-). There is a whole Journal devoted
to things magnetic, with lots of studies of interesting compounds. But
from a practical perspective, it is worth noting that some magnetic tapes
have a rated shelf life of 8-10 years while enterprise-class backup tapes
are only rated at 30 years. Most disks have an expected operational life
of 5 years or so. As Tim notes, it is a good idea to plan for migrating
important data to newer devices over time.
-- richard
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