On Thu, Jun 2, 2011 at 9:39 PM, Dave Chinner <david@xxxxxxxxxxxxx> wrote: > On Thu, Jun 02, 2011 at 08:42:47PM -0400, Christoph Hellwig wrote: >> On Thu, Jun 02, 2011 at 10:42:46AM -0400, Paul Anderson wrote: >> > This morning, I had a symptom of a I/O throughput problem in which >> > dirty pages appeared to be taking a long time to write to disk. >> > >> > The system is a large x64 192GiB dell 810 server running 2.6.38.5 from >> > kernel.org - the basic workload was data intensive - concurrent large >> > NFS (with high metadata/low filesize), rsync/lftp (with low >> > metadata/high file size) all working in a 200TiB XFS volume on a >> > software MD raid0 on top of 7 software MD raid6, each w/18 drives. I >> > had mounted the filesystem with inode64,largeio,logbufs=8,noatime. >> >> A few comments on the setup before trying to analze what's going on in >> detail. I'd absolutely recommend an external log device for this setup, >> that is buy another two fast but small disks, or take two existing ones >> and use a RAID 1 for the external log device. This will speed up >> anything log intensive, which both NFS, and resync workloads are lot. >> >> Second thing if you can split the workloads into multiple volumes if you >> have two such different workloads, so thay they don't interfear with >> each other. >> >> Second a RAID0 on top of RAID6 volumes sounds like a pretty worst case >> for almost any type of I/O. You end up doing even relatively small I/O >> to all of the disks in the worst case. I think you'd be much better >> off with a simple linear concatenation of the RAID6 devices, even if you >> can split them into multiple filesystems >> >> > The specific symptom was that 'sync' hung, a dpkg command hung >> > (presumably trying to issue fsync), and experimenting with "killall >> > -STOP" or "kill -STOP" of the workload jobs didn't let the system >> > drain I/O enough to finish the sync. I probably did not wait long >> > enough, however. >> >> It really sounds like you're simply killloing the MD setup with a >> log of log I/O that does to all the devices. > > And this is one of the reasons why I originally suggested that > storage at this scale really should be using hardware RAID with > large amounts of BBWC to isolate the backend from such problematic > IO patterns. > Dave Chinner > david@xxxxxxxxxxxxx > Good HW RAID cards are on order - seems to be backordered at least a few weeks now at CDW. Got the batteries immediately. That will give more options for test and deployment. Not sure what I can do about the log - man page says xfs_growfs doesn't implement log moving. I can rebuild the filesystems, but for the one mentioned in this theread, this will take a long time. I'm guessing we'll need to split out the workload - aside from the differences in file size and use patterns, they also have fundamentally different values (the high metadata dataset happens to be high value relative to the low metadata/large file dataset). Paul _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
