Paul B. Henson wrote:
On Wed, 20 May 2009, Darren J Moffat wrote:
Why do you think there is no progress ?
Sorry if that's a wrong assumption, but I posted questions regarding it to
this list with no response from a Sun employee until yours, and the
engineer assigned to my support ticket was unable to provide any
information as to the current state or if anyone was working on it or why
it was so hard to do. Barring any data to the contrary it appeared from an
external perspective that it was stalled.
How Sun Services reports the status of escalations to customers under
contract is not a discussion for a public alias like this so I won't
comment on this.
The code for this is hard to implement. People are working on very hard
but that doesn't mean there isn't any progress if there is no eta or
workaround available via Sun Service.
Why is it so hard? I understand that removing a data vdev or shrinking the
size of a pool is complicated, but what makes it so difficult to remove a
slog? If the slog fails the pool returns to an embedded log, it seems the
only difference between a pool with a failed slog and a pool with no slog
is that the former knows it used to have a slog. Why is it not as simple as
updating the metadata for a pool with a failed slog so it no longer thinks
it has a slog?
If the engineers that are working on this wish to comment I'm sure they
will, but I know it really isn't that simple.
On another note, do you have any idea how one might recover from the case
where a slog device fails while the pool is inactive and renders it
inaccessible?
I do; because I've done it to my own personal data pool. However it is
not a procedure I'm willing to tell anyone how to do - so please don't
ask - a) it was highly dangerous and involved using multiple different
zfs kernel modules was well as updating disk labels from inside kmdb and
b) it was several months ago and I think I'd forget a critical step.
I'm not even sure I could repeat it on a pool with a non trivial number
of datasets. It did how ever give me an appreciation for the issues in
implementing this for a generic solution in a way that is safe to do and
that works for all types of pool and slog config (mine was a very simple
configuration: mirror + slog).
--
Darren J Moffat
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