On Apr 28, 2009, at 18:02, Richard Elling wrote:
Kees Nuyt wrote:
Some high availablility storage systems overcome this decay
by not just reading, but also writing all blocks during a
scrub. In those systems, scrubbing is done semi-continously
in the background, not on user/admin demand.
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
really want to be sure the data is correct before you rewrite.
Neither
is completely foolproof, so it is still a good idea to have
backups :-)
Hopefully bp relocate will be make it into Solaris at some point, so
when a scrub gets kicked off we'll be able to have that (at least as
an option, if not by default).
Mac OS 10.5 auto-defrags in the background (given certain criteria are
met), but iHFS+ doesn't have checksums, so there's a bit risk in
creating errors.
Combine the two and you have a fairly robust defrag system.
_______________________________________________
zfs-discuss mailing list
zfs-discuss@opensolaris.org
http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
