Tim wrote:
On Fri, Feb 13, 2009 at 4:21 PM, Bob Friesenhahn
<bfrie...@simple.dallas.tx.us <mailto:bfrie...@simple.dallas.tx.us>>
wrote:
On Fri, 13 Feb 2009, Ross Smith wrote:
However, I've just had another idea. Since the uberblocks are
pretty
vital in recovering a pool, and I believe it's a fair bit of
work to
search the disk to find them. Might it be a good idea to
allow ZFS to
store uberblock locations elsewhere for recovery purposes?
Perhaps it is best to leave decisions on these issues to the ZFS
designers who know how things work.
Previous descriptions from people who do know how things work
didn't make it sound very difficult to find the last 20
uberblocks. It sounded like they were at known points for any
given pool.
Those folks have surely tired of this discussion by now and are
working on actual code rather than reading idle discussion between
several people who don't know the details of how things work.
People who "don't know how things work" often aren't tied down by the
baggage of knowing how things work. Which leads to creative solutions
those who are weighed down didn't think of. I don't think it hurts in
the least to throw out some ideas. If they aren't valid, it's not
hard to ignore them and move on. It surely isn't a waste of anyone's
time to spend 5 minutes reading a response and weighing if the idea is
valid or not.
OTOH, anyone who followed this discussion the last few times, has looked
at the on-disk format documents, or reviewed the source code would know
that the uberblocks are kept in an 128-entry circular queue which is 4x
redundant with 2 copies each at the beginning and end of the vdev.
Other metadata, by default, is 2x redundant and spatially diverse.
Clearly, the failure mode being hashed out here has resulted in the defeat
of those protections. The only real question is how fast Jeff can roll
out the
feature to allow reverting to previous uberblocks. The procedure for doing
this by hand has long been known, and was posted on this forum -- though
it is tedious.
-- richard
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