[sheepdog] question about journaling

[MORITA Kazutaka]

At Sun, 1 Sep 2013 23:39:03 +0800,
Dong Wu wrote:
> 
> hi all, I hava a question about journaling performance.
> when journal is on, data is written to both journal file and backend
> store, how journal can boost write performance compare to normal
> write(just write to backend store)?

Journaling boosts random write performance.

When journaling is enabled, data is written to journal file with
O_DSYNC and to backend store without O_DSYNC.  Journaling writes are
basically sequential.  If sequential writes result in a better
performance than random ones on your disks, it will boost the
performance.

Thanks,

Kazutaka