Samsung EVO 850 500g + pe2950/PERC6/i = poor perf

[Karandras]

Hey,

So building a server for a client we decided to dive into the realm of SSDs. Found the Samsung EVO 850 500g drive on sale for under $250 so I was sold on that. Here are my settings on the Perc6/i controller (with the most recent firmware):

RAID0
1 x Samsung EVO 850 500g
Stripe Size = 256k (tried 64k with even worse performance)
Read Ahead
Write Back (with Battery Backup)

OS = CentOS 6.6 with yum updated

I don't see an option in the Perc6/i controller to allow the drive straight through so it required a RAID0 setup with only one drive. I understand I'm not using enterprise drives but we can't afford to put Dell SSDs in such an old server.

With the current setup here are my results ( got the test from here http://askubuntu.com/questions/87035/how-to-check-hard-disk-performance ):

dd if=/dev/zero of=/tmp/output conv=fdatasync bs=384k count=1k; rm -f /tmp/output
1024+0 records in
1024+0 records out
402653184 bytes (403 MB) copied, 2.62329 s, 153 MB/s

dd if=/dev/zero of=/tmp/output conv=fdatasync bs=384k count=10k; rm -f /tmp/output
10240+0 records in
10240+0 records out
4026531840 bytes (4.0 GB) copied, 29.5543 s, 136 MB/s

dd if=/dev/zero of=/tmp/output conv=fdatasync bs=4k count=1000k; rm -f /tmp/output
1024000+0 records in
1024000+0 records out
4194304000 bytes (4.2 GB) copied, 30.8807 s, 136 MB/s


While those results at 256k Stripe are double the speed of 64k stripe they still seem very slow in comparison to what this drive advertises what it can do. Would the stripe size be the problem still? The new firmware for the Perc6/i lets me do 512k and 1M stripes.

Am I stuck with that because of the age of the card? From what I understand this card can do over 500 MB/sec...

Thanks!

 

[Karandras]

Found some more tests here (http://linuxconfig.org/hard-drive-speed-test-using-linux-command-line-and-hdparm) with hdparm:

hdparm -t /dev/sda

/dev/sda:
Timing buffered disk reads: 836 MB in 3.01 seconds = 278.06 MB/sec
[root@114-029-180-199-av1 ~]# hdparm -t --direct /dev/sda

/dev/sda:
Timing O_DIRECT disk reads: 878 MB in 3.00 seconds = 292.42 MB/sec
[root@114-029-180-199-av1 ~]# hdparm --offset 50 -t /dev/sda

/dev/sda:
Timing buffered disk reads (offset 50 GB): 2554 MB in 3.00 seconds = 851.15 MB/sec
[root@114-029-180-199-av1 ~]# hdparm --offset 50 -T /dev/sda

/dev/sda:
Timing cached reads: 15022 MB in 2.00 seconds = 7521.84 MB/sec


Why are these numbers so much different?