I have a 30TB XFS filesystem created on CentOS 5.4 X86_64, kernel 2.6.39, using xfsprogs 2.9.4. The underlying hardware is 12 3TB SATA drives on a Dell PERC 700 controller with 1GB cache. There is an external journal on a separate set of 15k SAS drives (I suspect now this was unnecessary, because there is very little metadata activity). When I created the filesystem I (mistakenly) believed the stripe width of the filesystem should count all 12 drives rather than 11. I've seen some opinions that this is correct, but a larger number which have convinced me that it is not. I also set up the RAID BIOS to use a small stripe element of 8KB per drive, based on the I/O request size I was seeing at the time in previous installations of the same application, which was generally doing writes around 100KB. l'm trying to determine how to proceed to optimize write performance. Recreating the filesystem and its existing data is not out of the question, but would be a last resort. The filesystem contains a MongoDB installation consisting of roughly 13000 2GB files which are already allocated. The application is almost exclusively inserting data, there are no updates, and files are written pretty much sequentially. When I set up the fstab entry I believed that it would inherit the stripe geometry automatically, however now I understand that is not the case with XFS version 2. What I'm seeing now is average request sizes which are about 100KB, half the stripe size. With a typical write volume around 5MB per second I am getting wait times around 50ms, which appears to be degrading performance. The filesystem was created on a partition aligned to a 1MB boundary. Short of recreating the filesystem with the correct stripe width, would it make sense to change the mount options to define a stripe width that actually matches either the filesystem (11 stripe elements wide) or the hardware (12 stripe elements wide)? Is there a danger of filesystem corruption if I give fstab a mount geometry that doesn't match the values used at filesystem creation time? I'm unclear on the role of the RAID hardware cache in this. Since the writes are sequential, and since the volume of data written is such that it would take about 3 minutes to actually fill the RAID cache, I would think the data would be resident in the cache long enough to assemble a full-width stripe at the hardware level and avoid the 4 I/O RAID5 penalty. -- View this message in context: http://old.nabble.com/How-to-deal-with-XFS-stripe-geometry-mismatch-with-hardware-RAID5-tp33498437p33498437.html Sent from the Xfs - General mailing list archive at Nabble.com. _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
