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
--
To unsubscribe from this list: send the line "unsubscribe
linux-raid" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
<mailto:majordomo@xxxxxxxxxxxxxxx>
More majordomo info at http://vger.kernel.org/majordomo-info.html
--
Roberto Spadim
--
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
