Question

LSI MegaRaid Write Performance Horrible

Asked by: akaSurreal

My new SCSI RAID setup is performing very poorly on write speeds and I don't understand why.  And, no it's not just a simple WRITE-BACK fix either =)

Here is what I have:

Dell PowerEdge 2850
Dual Xeon 3.2Ghz
8GB RAM
LSI MegaRAID 320-4X (Quad Channel) 256MB with BBU
6 x 36GB Seagate 15K SCSI

Dell PowerVault PV220S/PV221S
14 x 36GB Seagate 15K SCSI

OS: Windows - 2003

RAID Config:

PowerVault in split bus mode.
Two external connections from Channel 1 & 2 of Raid Controller
14 x Raid 10

Channel 0 is being used for internal drives on 2850 for OS and Hotspares.

I am using IO Meter with unpartitioned drives for testing:

14xRaid10
8K Streaming Read test, I peak with 60,894 IOps (475MB/sec) at 256 Concurrent IO's.
8K Streaming Write test, I peak with 18,636 IOps (145MB/sec) at 32 Concurrent IO's.

I tried with WRITE-BACK and WRITE-THROUGH with seemingly very little difference.  I understand WRITE-BACK is supposed to be the faster mode because of the lazy writes.  I also understand that my speed should go down on writing, but with a Single Drive Speed (2xRaid1) I can get 80MB/sec sustained (vs 90MB for read), but with 14xRaid10 I only get 145?  That does not add up.

I have also tried using HD-Speed from www.steelbytes.com and I get similiar results to IO Meter sequential tests if I set my block size to 1MB (16MB for read).

So here's my questions:

1) Primary Question, What is up with my write speed?
2) Is there any benefit to what channels I use on my Quad Channel controller.  Right now I am using 1 & 2 for the PowerVault, would 2 & 3 offer any changes good/bad/otherwise?  I assume 0/1 are controlled by one chip, 2/3 by another?
3) Is it normal to need so many Concurrent IO's (256) or on HD Speed, a 16MB Block size, to max out my read speed?  I have talked to a friend with a 14xRaid10 SATA RAID setup that does not need anywhere near 256IOs or 16MB BlockSize to get their peak speeds.

Thank you very much for any help you can give.

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Asked On
2006-08-19 at 14:58:37ID21960411
Tags

megaraid

,

lsi

,

write

,

performance

Topic

Hard Drives & Storage

Participating Experts
3
Points
500
Comments
34

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