On Mon, Nov 11, 2013 at 03:53:14PM -0200, Carlos Maiolino wrote: > On Mon, Nov 11, 2013 at 06:25:13PM +0100, Bernd Schubert wrote: > > Hi all, > > > > for streaming writes onto a raid6 the current round-robin ag > > selection seems does not seem to be optimal. Writing 4 files from 4 > > threads into a single directory we get 900 MB/s, writing 4 files in > > 4 different directories we only get 700 MB/s (12 disks with with hw > > megaraid-sas). The current round-robin scheme seems to be optimized > > for linear raid0? With small AGs one could also argue, that choosing > > AGs which are not far away from each other (in respect to the number > > of blocks) also adds more parallel disk access for small and medium > > sized files. > > > > Any objections against a patch to improve the AG selection? > > > > I wouldn't say this it is optimized specifically for raid 0 environments but I > lack some knowledge on this choice. The mainly reason for the round-robing IIRC, > was to avoid lock contention in a single AG. spreading different files along the > whole disk, and also making it able to allocate them contiguously along the disk. > Lock contention in inodes and blocks B-Trees for example, improving parallelism in the filesystem, but of course this might not be the optimal behavior for all environments. That's why XFS has a long list of tuning mkfs/mount options :-) > But, I'm not sure what kind of optimization you have in mind and I believe > another engineers will also need some extra information about what optimization > you have in mind, what kind of tests you're doing (Direct I/O, buffered, > pre-allocation), etc.. You'll also need to post filesystem configurations like > FS aligment (su, sw options), etc. > > For different write patterns, you might also want to take a look at the > rotor_step procfs option, and some other options dedicated to streaming writes, > that might help you in this case. > > Just my $0.02 > > > Just complementing my past comment -- Carlos _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
