Separate common journal device

[Andreas Dilger]

On May 27, 2004  12:59 -0700, M K wrote:
> Oh, good point.. BTW,  what should the ideal size of a
> journal be ? is there a general guideline to follow ?
> I am sort-of a newbie to ext3, any advice on choosing
> the journal size would be great!

It hasn't really been discussed much.  I'd benchmark with your apps to
see what is best.  For Lustre (which often has hundreds of clients doing
large IOs to a single ext3 filesystem at one time) we use the largest
journal size possible (400MB) to reduce the possibility that the clients
get blocked waiting for journal space.  Lustre creates very large journal
transactions so having a larger journal means we can have more concurrent
handles open and definitely improved performance.  Most of our server nodes
also have gobs of RAM, so journal size isn't much of an issue.

For other apps there is probably some upper limit where the journal never
really gets too full, and making it larger doesn't help much.  It also
slows down journal recovery a bit with a very large journal.

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