Author Topic: RT Raid - Performance issue  (Read 2520 times)

Offline itguy101

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RT Raid - Performance issue
« on: February 21, 2013, 01:24:00 pm »
I created a new RT array, 4xDRU + 1xPPU. Drives are fairly quick Hitachi 2tb 7200rpm capable of sustaining ~125MBps writes directly. In snapshot+pool mode (TX engine) I get ~115MBps, which is acceptable. However if I am using realtime raid (T1 engine), I max out at ~60MBps which is completely unacceptable. In RT mode, the Flexraid process is using around 18% CPU and 300mb ram.
This is on a Phenom II 965 with 8gb ram, so CPU and Ram should not be a limiting factor. Drives are attached via an LSI 2008 based HBA card, drives are in a 16bay SGI SAS expander.

Is this typical of the performance drop? What should I try to improve the throughput?

Offline Brahim

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Re: RT Raid - Performance issue
« Reply #1 on: February 21, 2013, 02:03:48 pm »
It all depends on what you are writing.
If many files, then yeah, there is a slow down due to the need to update the RT file system databases.
If a single large file that is pre-allocated, performance shouldn't fall off to hard.

Non pre-allocated files create fragmentation, which also has a performance hit.

Offline itguy101

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Re: RT Raid - Performance issue
« Reply #2 on: February 21, 2013, 03:05:43 pm »
I am copying my Movie rips so, many large files 4GB-40GB. Approximately 2TB at a time in a single copy job. The I used the same files to gauge the speeds I posted in the originating post.
I am using stock windows explorer to do the copy, which I believe does pre-allocate.
I was/am expecting a performance hit with RT, ~20-30MBps would be on the high side of acceptable.. but getting less than half of the bare drive throughput is not.

One, thought I had was it could possibly be my AV (eset) is scanning all writes to the RT database. Alas I haven't be able to test that theory yet as I had already switched to snapshot mode, I will switch back to RT and make those changes and let you know how that works out. In the meantime is there anything else that can improve throughput in RT mode?

Offline Brahim

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Re: RT Raid - Performance issue
« Reply #3 on: February 21, 2013, 04:12:20 pm »
Is your parity drive your fastest drive?
If not, that's a key improvement you can make as that's your true bottleneck.

People tend to use the worst drive in the array for parity, which is a bad approach.

Offline itguy101

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Re: RT Raid - Performance issue
« Reply #4 on: February 21, 2013, 06:07:42 pm »
All drives, including the parity are matching, 7200rpm hitachi 2tb drives. All are thoroughly tested and running the newest firmwares. They also came straight out of a working hardware raid 5 array.