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.
