On Wed, Jul 06, 2011 at 02:04:03PM +1000, Dave Chinner wrote: > > Although is there supposed to be a performance benefit from having > > a separate log disk with XFS? > > There used to be. Now everyone just uses delayed logging, which is > far faster and more scalable that even using an external log. Even with delayed logging external logs are a huge benefit if you hit the log hard, e.g. for fsync intensive workloads. E.g. when using fs_mark in fsync mode it gives speedups over 100% for the setups I've tested. You'll see similar speedups for NFS server loads that are log force heavy as well. > > > IIRC it has a disadvantage that you can't use barriers properly. > > That mostly works now (recent kernels), but you take a hit in > journal IO waiting synchronously for the data device caches to be > flushed before writing to the log device. For metadata-heavy workloads where an external log benefits you most you generally just want to disable the volatile write cache anyway. _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
