Separate common journal device

[Andreas Dilger]

On May 24, 2004  12:45 -0700, M K wrote:
> On a related note, wouldnt it be more efficient to
> have a single dedicated hard drive, with multiple
> partitions to store journals - one for each ext3
> system? 

No, because then each filesystem would cause seeking to its part of the
journal for each transaction (unless the dedicated device was NVRAM).
In general, the writes to the journal are pure overhead unless you
actually crash so they need to be as efficient as possible at write time
and the complexity at recovery time is much less critical.

Having all of the journal writes for multiple filesystems stream to a
single block device without any seeking is the best.  Making a larger
journal also helps a lot in the performance area, but you can't always
afford to consume so much RAM on a system (especially a larger journal
for each filesystem).

> --- Andreas Dilger <adilger at clusterfs.com> wrote:
> > It is possible now to use an external block device
> > for a single filesystem.
> > The on-disk format is designed to allow multiple
> > filesystems to share the
> > same device, but that has never been fully
> > implemented.

Cheers, Andreas
--
Andreas Dilger
http://sourceforge.net/projects/ext2resize/
http://www-mddsp.enel.ucalgary.ca/People/adilger/