Re: Description of the Journaling topology

[Gary Thorpe <gathorpe79@xxxxxxxxx>]

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.
>
> Rahul

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.