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From Peter Schuller <peter.schul...@infidyne.com>
Subject Re: Backup/Restore: Coordinating Cassandra Nodetool Snapshots with Amazon EBS Snapshots?
Date Thu, 23 Jun 2011 16:34:45 GMT
> that with storage, there are *lots* of urban legends and people making
> strange claims. In this case it is wrong for fundamental reasons
> independent of kernel implementation details.

Also, note that it is not specific to log based file systems. Even
"old" file systems the predates journaling or softupdates, were
specifically and carefully designed such that I/O was performed in a
way that would yield a recoverable state after a crash (this is why
'fsck' runs on boot on old systems). fsck was never primarily intended
to fix arbitrary corruption; file systems were written to perform I/O
in very careful ways (careful with respect to ordering of I/O
operations) such that a crash/reboot/power outage results in an
on-disk state which is recoverable to be consistent, *WITHOUT*
arbitrary data loss or corruption in the file system.

A journaling file system is just another method of achieving certain
goals, including crash consistency. It still relies on the same
fundamental properties of the underlying storage device.

-- 
/ Peter Schuller

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