DragonFly BSD
DragonFly kernel List (threaded) for 2004-12
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Re: Description of the Journaling topology

From: Gary Thorpe <gathorpe79@xxxxxxxxx>
Date: Wed, 29 Dec 2004 23:35:02 -0500

Rahul Siddharthan wrote:
I'm no expert but I thought the traditional case was fast recovery to
a consistent filesystem state (avoiding a long fsck), not recovery of
buffered data or fast writing of buffered data to disk.  I'm pretty
sure ext3, for example, with its default async mount, is very
susceptible to losing data.  ufs+softupdates most certainly can lose a
lot of buffered data.


A buffer is not a journal, its a buffer. Journaling file systems put the journal ON DISK--if power is lost you replay the journal FROM DISK to recover consistent file system. This scheme will not allow that because the journal is kept in memory. You can use it for transparent backup, but how useful is it for recovery from crashes/power loss? It seems like transaction based VFS mirroring, but you cannot replay the journal if the system crashes or otherwise reboots unexpectedly.

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