On 11/11/2013 06:55 PM, Carlos Maiolino wrote: > 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 Agreed, more locks help to avoid that. > 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. One of my colleagues benchmarked this on one of our fast systems and another colleague current needs this system for other tests, so I don't have the exact parameters. However, it was for sure formated with options like these: mkfs.xfs -d su=256k,sw=10 -l version=2,su=256k -isize=512 /dev/sdX and mounted with these options: mount -onoatime,nodiratime,largeio,inode64,swalloc,allocsize=131072k,nobarrier /dev/sdX <mountpoint> >> >> 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. Thanks, I didn't know that knob, I'm going to look into it. According to the comments its for inode32 only, but I need to read the xfs_alloc code first to see what it actually does. Thanks, Bernd _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
