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What is going on here?! I am baffled.

serveradmin@FILESERVER:/Volumes/MercuryInternal/test$ sudo dd if=/dev/zero of=/Volumes/MercuryInternal/test/test.fs bs=4096k count=10000
10000+0 records in
10000+0 records out
41943040000 bytes (42 GB) copied, 57.0948 s, 735 MB/s
serveradmin@FILESERVER:/Volumes/MercuryInternal/test$ sudo dd if=/Volumes/MercuryInternal/test/test.fs of=/dev/null bs=4096k count=10000
10000+0 records in
10000+0 records out
41943040000 bytes (42 GB) copied, 116.189 s, 361 MB/s

OF NOTE: My RAID50 is 3 sets of 8 disks. - This might not be the best config for SPEED.

OS: Ubuntu 12.04.1 x64
Hardware Raid: RocketRaid 2782 - 24 Port Controller
HardDriveType: Seagate Barracuda ES.2 1TB
Drivers: v1.1 Open Source Linux Drivers.

So 24 x 1TB drives, partitioned using parted. Filesystem is ext4. I/O scheduler WAS noop but have changed it to deadline with no seemingly performance benefit/cost.

serveradmin@FILESERVER:/Volumes/MercuryInternal/test$ sudo gdisk -l /dev/sdb
GPT fdisk (gdisk) version 0.8.1

Partition table scan:
  MBR: protective
  BSD: not present
  APM: not present
  GPT: present

Found valid GPT with protective MBR; using GPT.
Disk /dev/sdb: 41020686336 sectors, 19.1 TiB
Logical sector size: 512 bytes
Disk identifier (GUID): 95045EC6-6EAF-4072-9969-AC46A32E38C8
Partition table holds up to 128 entries
First usable sector is 34, last usable sector is 41020686302
Partitions will be aligned on 2048-sector boundaries
Total free space is 5062589 sectors (2.4 GiB)

Number  Start (sector)    End (sector)  Size       Code  Name
   1            2048     41015625727   19.1 TiB    0700  primary

To me this should be working fine. I can't think of anything that would be causing this other then fundamental driver errors? I can't seem to get much/if any higher then the 361MB a second, is this hitting the "SATA2" link speed, which it shouldn't given it is a PCIe2.0 card. Or maybe some cacheing quirk - I do have Write Back enabled.

Does anyone have any suggestions? Tests for me to perform? Or if you require more information, I am happy to provide it!

This is a video fileserver for editing machines, so we have a preference for FAST reads over writes. I was just expected more from RAID 50 and 24 drives together...

EDIT: (hdparm results)

serveradmin@FILESERVER:/Volumes/MercuryInternal$ sudo hdparm -Tt /dev/sdb

 Timing cached reads:   17458 MB in  2.00 seconds = 8735.50 MB/sec
 Timing buffered disk reads: 884 MB in  3.00 seconds = 294.32 MB/sec

EDIT2: (config details)

Also, I am using a RAID block size of 256K. I was told a larger block size is better for larger (in my case large video) files. WEBGUI SCREENSHOT

EDIT3: (Bonnie++ Results. Would love some guidance with this!)

Bonnie++ Results

share|improve this question
Many systems cheat when you write nothing but zeroes to them. Try creating a large file of random data and using that file as a source when testing, or using a "better" test like hdparm. –  Chris S Nov 12 '12 at 1:45
I did try hdparm, but it only tested for reads in all the guides I read, and it only read for something like 2 seconds? My understanding is you need a big file (double your RAM) to eliminate any possibility of cacheing? –  James Nov 12 '12 at 1:47

1 Answer 1

Please use a purpose-built benchmarking tool like Iozone to get a better feel for the real performance of the system. All too often, I see people using dd to benchmark. It's not a good representation of real-life I/O workloads.

Based on the results of an Iozone test, I'd probably look at the caching situation and possibly if you have any barriers enabled. This is strange because your issue seems to be read speed. Hmm...

You're definitely not hitting the limits of the SAS/SATA link. You do have 24 end-to-end connections, right? There's no SAS expander in the mix, correct?

share|improve this answer
Also try bonnie++ for benchmarking. Available from apt-get. –  John Siu Nov 12 '12 at 2:23
I think I am correct in saying they all have end to end connections to the card? There are 6 SFF-8087 cables supporting 4 drives per cable. No expanders as I understand them to mean a separate card? This is direct from the RocketRaid to the backplane of the raid chassis. So 4 drives per cable. Should be all "electrically" connected 100%. I am using a NORCO RPC-4224. I will look into Iozone. –  James Nov 12 '12 at 2:23

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