max journal size
pegasus at nerv.eu.org
Thu Feb 16 09:23:39 UTC 2006
On Wed, 15 Feb 2006 13:52:38 -0700
Andreas Dilger <adilger at clusterfs.com> wrote:
> The limit exists to avoid users making the journal too large and consuming
> all of their RAM with pinned buffers while the journal is commiting buffers
> to the journal and checkpointing them to disk. Under heavy load it is
> possible for jbd to have 3/4*journal_size of lowmem pinned.
> This limit does not apply when using an external journal.
Excellent. So that means I can use any size for external journal.
Next question ... the point of having ssd for journal is forcing as much io through it as possible, especially writes. Default journal commit is something like 5 seconds, yes? My application - busy mail gateway - would imho bennefit from much larger journal commit times. As I understand, jounral commit is atomic operation - nothing else can do io to that filesystem at the same time. With large journals and long time between commits, the commit itself takes a measureable amount of time. What happens if I pull the plug during such commit? How well tested area is this?
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