From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrei Banu Subject: Re: Incredibly poor performance of mdraid-1 with 2 SSD Samsung 840 PRO Date: Sun, 21 Apr 2013 02:25:14 +0300 Message-ID: <517323DA.5010209@redhost.ro> References: <5171CBF9.9020701@redhost.ro> <51725458.7020109@redhost.ro> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: linux-raid@vger.kernel.org List-Id: linux-raid.ids The previous test was done with "noop" for scheduler (the speed test completed at about 8MB/s). Then I rebooted the server and redone the test (also with noop) and the result was slightly better but not as it should be (21MB/s). A third test 5-10 minute later (after the load subsided) completed at 16MB/s. A fourth test ended with 14.6MB/s. Something else: the weekly auto raid check started a little time ago and it's going at an average of 60MB/s (anywhere between 25 and 100MB/s) with noop, cfq and deadline. A raid check with ordinary mechanical drives gets done at about 160MB/s on the outer cylinders. Why are these SSDs so slow? These are the result from the 21MB/s test (5 seconds delay): Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn sda 204.94 1918.02 389.30 1367719 277605 sdb 154.80 1196.21 389.30 853008 277605 md1 0.65 2.59 0.00 1848 0 md2 355.45 3106.05 388.53 2214890 277056 md0 1.10 2.90 0.01 2069 9 Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn sda 583.40 42764.80 29452.90 213824 147264 sdb 234.80 23172.00 14950.50 115860 74752 md1 0.00 0.00 0.00 0 0 md2 8079.60 65886.40 29862.40 329432 149312 md0 0.00 0.00 0.00 0 0 Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn sda 15.00 1.60 1740.00 8 8700 sdb 15.00 0.00 7196.80 0 35984 md1 0.00 0.00 0.00 0 0 md2 333.20 1.60 1330.40 8 6652 md0 0.00 0.00 0.00 0 0 Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn sda 167.20 538.40 37432.80 2692 187164 sdb 86.20 16.00 33688.80 80 168444 md1 0.00 0.00 0.00 0 0 md2 9510.80 572.80 37934.40 2864 189672 md0 0.00 0.00 0.00 0 0 Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn sda 150.20 585.60 29090.40 2928 145452 sdb 71.20 44.00 30355.20 220 151776 md1 0.00 0.00 0.00 0 0 md2 7306.20 615.20 28998.40 3076 144992 md0 0.00 0.00 0.00 0 0 Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn sda 257.20 1624.00 9913.80 8120 49569 sdb 137.20 372.00 21438.60 1860 107193 md1 0.00 0.00 0.00 0 0 md2 2600.80 1991.20 9504.00 9956 47520 md0 0.00 0.00 0.00 0 0 Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn sda 186.80 972.80 292.70 4864 1463 sdb 150.40 733.60 292.70 3668 1463 md1 0.00 0.00 0.00 0 0 md2 283.80 1706.40 291.20 8532 1456 md0 0.00 0.00 0.00 0 0 If you have any idea what can I do to improve this please let me know. Thanks!!