2011-11-08 23:36, Bob Friesenhahn wrote:
On Tue, 8 Nov 2011, Jim Klimov wrote:
Second question regards single-HDD reliability: I can
do ZFS mirroring over two partitions/slices, or I can
configure "copies=2" for the datasets. Either way I
think I can get protection from bad blocks of whatever
nature, as long as the spindle spins. Can these two
methods be considered equivalent, or is one preferred
(and for what reason)?
Using two partitions on the same disk seems to give you most of the
headaches associated with more disks without much of the benefit. If
there is any minor issue, you will see zfs resilvering partitions and
resilvering will be slow due to the drive heads flailing back and forth
between partitions. There is also the issue that the block allocation is
not likely to be very efficient in terms of head movement if two
partitions are used.
Thanks, Bob, I figured so...
And would copies=2 save me from problems of data loss and/or
inefficient resilvering? Does all required data and metadata
get duplicated this way, so any broken sector can be amended?
I read on this list recently, that some metadata is already
"copies=2 or =3". To what extent?.. Should the trunk of the
ZFS block tree be expected always secured, even on one disk?
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