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 02:26:09 +0300 Message-ID: <51732411.40306@redhost.ro> References: <5171CBF9.9020701@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 Hi, I ran with '-d 3' iostat during a "heavy" (540MB) copy. It took a bit over a minute and completed with less than 9MB/s. These are some of the results (this does NOT include the first batch i.e. the average from start up result): Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn sda 503.00 1542.67 28157.33 4628 84472 sdb 66.00 72.00 13162.67 216 39488 md1 373.00 1492.00 0.00 4476 0 md2 6951.67 126.67 27734.67 380 83204 md0 0.00 0.00 0.00 0 0 Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn sda 56.67 20.00 1177.50 60 3532 sdb 47.33 12.00 10824.17 36 32472 md1 0.67 2.67 0.00 8 0 md2 322.00 25.33 1266.67 76 3800 md0 0.00 0.00 0.00 0 0 Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn sda 122.00 16.00 45773.33 48 137320 sdb 96.67 14.67 19472.00 44 58416 md1 0.00 0.00 0.00 0 0 md2 11431.00 32.00 45684.00 96 137052 md0 0.00 0.00 0.00 0 0 Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn sda 0.00 0.00 0.00 0 0 sdb 13.67 8.00 5973.33 24 17920 md1 0.00 0.00 0.00 0 0 md2 2.00 8.00 0.00 24 0 md0 0.00 0.00 0.00 0 0 This is the "normal" iostat took after 10 minutes (this DOES include the first batch i.e. the average from start up result): Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn sda 281.83 973.99 641.55 212615675 140045467 sdb 215.51 665.94 641.55 145369465 140045467 md1 1.18 2.17 2.56 473492 558452 md2 470.71 1596.29 638.01 348460340 139272912 md0 0.08 0.27 0.00 59983 171 Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn sda 41.67 237.33 133.67 712 401 sdb 39.33 90.67 133.67 272 401 md1 0.00 0.00 0.00 0 0 md2 83.00 328.00 133.33 984 400 md0 0.00 0.00 0.00 0 0 Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn sda 29.33 2.67 110.00 8 330 sdb 29.33 2.67 110.00 8 330 md1 0.00 0.00 0.00 0 0 md2 28.67 5.33 109.33 16 328 md0 0.00 0.00 0.00 0 0 Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn sda 175.67 1.33 747.50 4 2242 sdb 182.00 56.00 747.50 168 2242 md1 0.00 0.00 0.00 0 0 md2 191.33 57.33 746.67 172 2240 md0 0.00 0.00 0.00 0 0 Best regards! On 20/04/2013 3:59 AM, Roberto Spadim wrote: > run some kind of iostat -d 1 -k and check the write/read iops and kb/s > > > 2013/4/19 Andrei Banu > > > Hello! > > 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. > > Few examples: > > root [~]# dd if=testfile.tar.gz of=test20 oflag=sync bs=4M > 130+1 records in > 130+1 records out > 547682517 bytes (548 MB) copied, 7.99664 s, 68.5 MB/s > > And 10-20 seconds later I try the very same test: > > root [~]# dd if=testfile.tar.gz of=test21 oflag=sync bs=4M > 130+1 records in / 130+1 records out > 547682517 bytes (548 MB) copied, 52.1958 s, 10.5 MB/s > > A different test with 'bs=1G' > root [~]# w > 12:08:34 up 1 day, 13:09, 1 user, load average: 0.37, 0.60, 0.72 > > root [~]# dd if=testfile.tar.gz of=test oflag=sync bs=1G > 0+1 records in / 0+1 records out > 547682517 bytes (548 MB) copied, 75.3476 s, 7.3 MB/s > > root [~]# w > 12:09:56 up 1 day, 13:11, 1 user, load average: 39.29, 12.67, 4.93 > > It needed 75 seconds to copy a half GB file and the server load > increased 100 times. > > And a final test: > > root@ [~]# dd if=/dev/zero of=test24 bs=64k count=16k conv=fdatasync > 16384+0 records in / 16384+0 records out > 1073741824 bytes (1.1 GB) copied, 61.8796 s, 17.4 MB/s > > This time the load spiked to only ~ 20. > > A few other peculiarities: > > root@ [~]# hdparm -t /dev/sda > Timing buffered disk reads: 654 MB in 3.01 seconds = 217.55 MB/sec > root@ [~]# hdparm -t /dev/sdb > Timing buffered disk reads: 272 MB in 3.01 seconds = 90.44 MB/sec > > The read speed is very different between the 2 devices (the margin > is 140%) but look what happens when I run it with --direct: > > root@ [~]# hdparm --direct -t /dev/sda > Timing O_DIRECT disk reads: 788 MB in 3.00 seconds = 262.23 MB/sec > root@ [~]# hdparm --direct -t /dev/sdb > Timing O_DIRECT disk reads: 554 MB in 3.00 seconds = 184.53 MB/sec > > So the hardware seems to sustain speeds of about 200MB/s on both > devices but it differs greatly. > The measurement of sda increased 20% but sdb doubled. Maybe > there's a problem with the page cache? > > BACKGROUND INFORMATION > Server type: general shared hosting server (3 weeks new) > O/S: CentOS 6.4 / 64 bit (2.6.32-358.2.1.el6.x86_64) > Hardware: SuperMicro 5017C-MTRF, E3-1270v2, 16GB RAM, 2 x Samsung > 840 PRO 512GB > Partitioning: ~ 100GB left for over-provisioning, ext 4: > > I believe it is aligned: > > root [~]# fdisk -lu > > Disk /dev/sda: 512.1 GB, 512110190592 bytes > 255 heads, 63 sectors/track, 62260 cylinders, total 1000215216 sectors > Units = sectors of 1 * 512 = 512 bytes > Sector size (logical/physical): 512 bytes / 512 bytes > I/O size (minimum/optimal): 512 bytes / 512 bytes > Disk identifier: 0x00026d59 > > Device Boot Start End Blocks Id System > /dev/sda1 2048 4196351 2097152 fd Linux raid > autodetect > Partition 1 does not end on cylinder boundary. > /dev/sda2 * 4196352 4605951 204800 fd Linux raid > autodetect > Partition 2 does not end on cylinder boundary. > /dev/sda3 4605952 814106623 404750336 fd Linux raid > autodetect > > Disk /dev/sdb: 512.1 GB, 512110190592 bytes > 255 heads, 63 sectors/track, 62260 cylinders, total 1000215216 sectors > Units = sectors of 1 * 512 = 512 bytes > Sector size (logical/physical): 512 bytes / 512 bytes > I/O size (minimum/optimal): 512 bytes / 512 bytes > Disk identifier: 0x0003dede > > Device Boot Start End Blocks Id System > /dev/sdb1 2048 4196351 2097152 fd Linux raid > autodetect > Partition 1 does not end on cylinder boundary. > /dev/sdb2 * 4196352 4605951 204800 fd Linux raid > autodetect > Partition 2 does not end on cylinder boundary. > /dev/sdb3 4605952 814106623 404750336 fd Linux raid > autodetect > > The matrix is NOT degraded: > > root@ [~]# cat /proc/mdstat > Personalities : [raid1] > md0 : active raid1 sdb2[1] sda2[0] > 204736 blocks super 1.0 [2/2] [UU] > md2 : active raid1 sdb3[1] sda3[0] > 404750144 blocks super 1.0 [2/2] [UU] > md1 : active raid1 sdb1[1] sda1[0] > 2096064 blocks super 1.1 [2/2] [UU] > unused devices: > > Write cache is on: > > root@ [~]# hdparm -W /dev/sda > write-caching = 1 (on) > root@ [~]# hdparm -W /dev/sdb > write-caching = 1 (on) > > SMART seems to be OK: > SMART overall-health self-assessment test result: PASSED (for both > devices) > > I have tried changing IO scheduler with NOOP and deadline but I > couldn't see improvements. > > I have tried running fstrim but it errors out: > > root [~]# fstrim -v / > fstrim: /: FITRIM ioctl failed: Operation not supported > > So I have changed /etc/fstab to contain noatime and discard and > rebooted the server but to no avail. > > I no longer know what to do. And I need to come up with some sort > of a solution (it's not reasonable nor acceptable to get at 3 > digits loads from copying several GBs worth of file). If anyone > can help me, please do! > > Thanks in advance! > Andy > -- > To unsubscribe from this list: send the line "unsubscribe > linux-raid" in > the body of a message to majordomo@vger.kernel.org > > More majordomo info at http://vger.kernel.org/majordomo-info.html > > > > > -- > Roberto Spadim