On 11-Feb-09, at 9:30 PM, Uwe Dippel wrote:
Toby,
sad that you fall for the last resort of the marketing droids here.
All manufactures (and there are only a few left) will sue the hell
out of you if you state that their drives don't 'sync'. And each
and every drive I have ever used did. So the talk about a distinct
borderline between 'enterprise' and 'home' is just cheap and not
sustainable.
They have existed. This thread has shown a motive to verify COTS
drives for this property, if the data is valuable.
Also, if you were correct, and ZFS allowed for compromising the
metadata of dormant files (folders) by writing metadata for other
files (folders), we would not have advanced beyond FAT, and ZFS
would be but a short episode in the history of file systems. Or am
I the last to notice that atomic writes have been dropped?
Especially with atomic writes you either have the last consistent
state of the file structure, or the updated one. So what would be
the meaning of 'always consistent on the drive' if metadata were
allowed to hang in between; in an inconsistent state? You write
"What is known, is the last checkpoint." Exactly, and here a
contradiction shows: the last checkpoint of all untouched files
(plus those read only) does contain exactly all untouched files.
How could one allow to compromise the last checkpoint by writing a
new one?
ZFS claims that the last checkpoint (my term, sorry, not an official
one) is fully consistent (metadata *and* data! Unlike other
filesystems). Since consistency is achievable by thousands of other
transactional systems I have no reason to doubt that it is achieved
by ZFS.
You are correct with "the feasible recovery mode is a partial".
Though here we have heard some stories of total loss. Nobody has
questioned that the recovery of an interrupted 'write' must
necessarily be partial. What is questioned is the complete loss of
semantics.
Only an incomplete transaction would be lost, AIUI. That is the
'atomic' property of all journaled and transactional systems. (All of
it, or none of it.)
--Toby
Uwe
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