On 11-Feb-09, at 7:16 PM, Uwe Dippel wrote:
I need to disappoint you here, LED inactive for a few seconds is a
very bad indicator of pending writes. Used to experience this on a
stick on Ubuntu, which was silent until the 'umount' and then it
started to write for some 10 seconds.
On the other hand, you are spot-on w.r.t. 'umount'. Once the
command is through, there is no more write to be expected. And if
there was, it would be a serious bug.
Yes; though at the risk of repetition - the bug here can be in the
drive...
So this 'umount'ed system needs to be in perfectly consistent
states. (Which is why I wrote further up that the structure above
the file system, that is the pool, is probably the culprit for all
this misery.)
[i]Conversely, anybody who is pulling disks / memory sticks off
while IO is
visibly incomplete really SHOULD expect to lose everything on them[/i]
I hope you don't mean this. Not in a filesystem much hyped and much
advanced. Of course, we expect corruption of all files whose
'write' has been boldly interrupted. But I for one, expect the
metadata of all other files to be readily available. Kind of, at
the next use, telling me:"You idiot removed the plug last, while
files were still in the process of writing. Don't expect them to be
available now. Here is the list of all other files: [list of all
files not being written then]"
That hope is a little naive. AIUI, it cannot be known, thanks to the
many indeterminacies of the I/O path, which 'files' were partially
written (since a whole slew of copy-on-writes to many objects could
have been in flight, and absent a barrier it cannot be known post
facto which succeeded). What is known, is the last checkpoint. Hence
the feasible recovery mode is a partial, automatic rollback to a past
consistent state.
Somebody correct me if I am wrong.
--Toby
Uwe
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