Hi!
They are connected through SATA2 ports (this does explain the read speed
but not the pitiful write one) in AHCI.
Ok, I redid the test with '-d 6' seconds and 'noop' scheduler during the
same file copy and these are the entire results:
root [~]# iostat -d 6 -k
Linux 2.6.32-358.2.1.el6.x86_64 (host) 04/21/2013 _x86_64_(8 CPU)
Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn
sda 245.95 832.69 591.13 219499895 155823699
sdb 190.80 572.24 590.88 150844446 155758671
md1 1.15 2.15 2.43 567732 641156
md2 406.02 1368.44 587.74 360725304 154930520
md0 0.06 0.23 0.00 59992 171
Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn
sda 34.17 0.00 4466.00 0 26796
sdb 9.67 0.00 4949.33 0 29696
md1 0.00 0.00 0.00 0 0
md2 1116.50 0.00 4466.00 0 26796
md0 0.00 0.00 0.00 0 0
Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn
sda 35.17 0.00 5475.33 0 32852
sdb 9.33 2.00 4522.67 12 27136
md1 0.00 0.00 0.00 0 0
md2 1369.67 8.00 5475.33 48 32852
md0 0.00 0.00 0.00 0 0
Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn
sda 40.33 0.00 3160.00 0 18960
sdb 19.50 0.00 7882.00 0 47292
md1 0.00 0.00 0.00 0 0
md2 790.50 2.67 3160.00 16 18960
md0 0.00 0.00 0.00 0 0
Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn
sda 77.67 4.00 15328.00 24 91968
sdb 50.33 16.00 10972.67 96 65836
md1 0.00 0.00 0.00 0 0
md2 3834.33 9.33 15328.00 56 91968
md0 0.00 0.00 0.00 0 0
Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn
sda 66.67 48.00 10604.00 288 63624
sdb 23.17 0.00 9660.00 0 57960
md1 0.00 0.00 0.00 0 0
md2 2653.50 51.33 10604.00 308 63624
md0 0.00 0.00 0.00 0 0
Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn
sda 37.83 24.67 5378.67 148 32272
sdb 13.17 3.33 6315.33 20 37892
md1 0.00 0.00 0.00 0 0
md2 1345.17 26.00 5378.67 156 32272
md0 0.00 0.00 0.00 0 0
Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn
sda 132.50 4.67 22714.00 28 136284
sdb 32.33 20.00 12328.00 120 73968
md1 0.00 0.00 0.00 0 0
md2 5713.67 31.33 22843.33 188 137060
md0 0.00 0.00 0.00 0 0
Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn
sda 58.17 6.00 8200.00 36 49200
sdb 23.00 8.00 11349.33 48 68096
md1 0.00 0.00 0.00 0 0
md2 1936.17 21.33 7729.33 128 46376
md0 0.00 0.00 0.00 0 0
Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn
sda 6.17 0.00 24.67 0 148
sdb 10.00 0.00 5120.00 0 30720
md1 0.00 0.00 0.00 0 0
md2 6.17 0.00 24.67 0 148
md0 0.00 0.00 0.00 0 0
Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn
sda 1.50 0.00 5.33 0 32
sdb 14.17 0.00 7170.67 0 43024
md1 0.00 0.00 0.00 0 0
md2 1.50 0.00 5.33 0 32
md0 0.00 0.00 0.00 0 0
Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn
sda 256.00 346.67 1105.17 2080 6631
sdb 270.83 544.00 7029.17 3264 42175
md1 49.33 170.00 27.33 1020 164
md2 311.83 705.33 1076.67 4232 6460
md0 0.00 0.00 0.00 0 0
Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn
sda 51.17 46.67 219.08 280 1314
sdb 48.67 140.00 219.08 840 1314
md1 20.67 82.67 0.00 496 0
md2 58.00 104.00 218.00 624 1308
md0 0.00 0.00 0.00 0 0
Thank you for your time.
Kind regards!
On 20/04/2013 4:11 PM, Roberto Spadim wrote:
Hum at beginning you have more iops than the end, how you connected
this devices, normally a ssd can handler more than 1000 iops and a hd
no more than 300iops, how did you configured the queue of ssd disks?
Could you change it to noop and test again?
Em 20/04/2013 05:39, "Andrei Banu" <andrei.banu@xxxxxxxxxx
<mailto:andrei.banu@xxxxxxxxxx>> escreveu:
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 <andrei.banu@xxxxxxxxxx
<mailto:andrei.banu@xxxxxxxxxx>>
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: <none>
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
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