Peter T. Breuer wrote:
ext3 journals are much safer on mirrored devices than on non-mirrored
That's irrelevant - you don't care what's in the journal, because if your system crashes before committal you WANT the data in the journal to be lost, rolled back, whatever, and you don't want your machine to have acked the write until it actually has gone to disk.
Or at least that's what *I* want. But then everyone has different
wants and needs. What is obvious, however, are the issues involved.
err, no.
If the journal is safely written to the journal device and the machine crashes whilst updating the main filesystem you want the journal to be replayed, not erased. The journal entries are designed to be replayable to a partially updated filesystem.
That's the whole point of journalling filesystems, write the deltas to the journal, make the changes to the fs, delete the deltas from the journal.
If the machine crashes whilst the deltas are being written then you won't play them back - but your fs will be consistent.
Journaled filesystems simply ensure the integrity of the fs metadata - they don't protect against random acts of application/user level vandalism (ie power failure).
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