On Fri December 18 2009, Bernd Schubert wrote: > On Saturday 19 December 2009, Matt Tehonica wrote: > > I have a 4 disk RAID5 using a 2048K chunk size and using XFS > > 4 disks is a bad idea. You should have 2^n data disks, but you have 2^1 + > 1 = 3 data disks. As parity information are calculated in the power of > two and blocks are written in the power of two, you probably have read > operations, when you only want to write. > > > filesystem. Typical file size is about 2GB-5GB. I usually get around > > 50MB/sec transfer speed when writting files to the array. Is this > > typcial or is it below normal? A friend has a 20 disk RAID6 using the > > same filesystem and chunk size and gets around 150MB/sec. Any input on > > this?? > > I would remove two disks, to get 16 + 2 drives (2^4). Performance > probably would be limited by CPU speed then. 150MB/s for 18 drives is > also bad, this is only the performance of two single raid0 drives. I'd have to agree. My 5 disk raid5 array gets me 200-400MB/s, depending on the kernel. I'm using a 512K chunk size, formatted with XFS, with 32 AGs, and xfs_info reporting: sunit=128 swidth=512 blks (which should be right...), and mounted with: noatime,nodiratime,logbufs=8,allocsize=512m,largeio,swalloc oh, not quite 200MB/s, iozone is showing 112MB/s write, and 300MB/s read. I'm pretty sure that has something to do with the writeback stuff though, and aught to be improved in 2.6.32+ (I have yet to find a good time to upgrade my server). I know I have seen the SAS card, and an initial array handle more throughput than that when I was first testing stuff months and months ago. It was more like 200-350 write, and 400-550 read. But yeah, 50MB/s is pretty bad for a raid array. The individual disks in my array are all capable of more than that each. (Yes, I know raid5 will not give a linear improvement when adding more drives, but it aught to be a heck of a lot better than a decrease in performance) > > Cheers, > Bernd > -- > To unsubscribe from this list: send the line "unsubscribe linux-raid" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- Thomas Fjellstrom tfjellstrom@xxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
