Forgot to CC the list. Sorry for the dup Andrei. On 4/19/2013 5:58 PM, Andrei Banu wrote: > I come to you with a difficult problem. We have a server otherwise > snappy fitted with mdraid-1 made of Samsung 840 PRO SSDs. If we copy a > larger file to the server (from the same server, from net doesn't > matter) the server load will increase from roughly 0.7 to over 100 (for > several GB files). Apparently the reason is that the raid can't write well. ... > 547682517 bytes (548 MB) copied, 7.99664 s, 68.5 MB/s > 547682517 bytes (548 MB) copied, 52.1958 s, 10.5 MB/s > 547682517 bytes (548 MB) copied, 75.3476 s, 7.3 MB/s > 1073741824 bytes (1.1 GB) copied, 61.8796 s, 17.4 MB/s > Timing buffered disk reads: 654 MB in 3.01 seconds = 217.55 MB/sec > Timing buffered disk reads: 272 MB in 3.01 seconds = 90.44 MB/sec > Timing O_DIRECT disk reads: 788 MB in 3.00 seconds = 262.23 MB/sec > Timing O_DIRECT disk reads: 554 MB in 3.00 seconds = 184.53 MB/sec ... Obviously this is frustrating, but the fix should be pretty easy. > O/S: CentOS 6.4 / 64 bit (2.6.32-358.2.1.el6.x86_64) I'd guess your problem is the following regression. I don't believe this regression is fixed in Red Hat 2.6.32-* kernels: http://www.archivum.info/linux-ide@xxxxxxxxxxxxxxx/2010-02/00243/bad-performance-with-SSD-since-kernel-version-2.6.32.html After I discovered this regression and recommended Adam Goryachev upgrade from Debian 2.6.32 to 3.2.x, his SSD RAID5 throughput increased by a factor of 5x, though much of this was due testing methods. His raw SSD throughput more than doubled per drive. The thread detailing this is long but is a good read: http://marc.info/?l=linux-raid&m=136098921212920&w=2 -- Stan -- 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
