BradI100
Enthusiast
Enthusiast

Radically different Read latency on same host and lun?

I have been running a lot of IOmeter tests on my shared storage connected via iSCSi.  I have two different guests 1 is a 2003 server the other is a plain XP Pro workstation.

On the server I get approximately 58 MBps read and write however, on the XP workstation I get 59MBps write but only 4.5MBps read.

They are on the same host.  They are on the same lun.  During testing I shut down one guest before testing the other and vice versa.

The read latency on the XP Pro vm is 10x than the write latency on the XP vm.  I am baffled any hints on where to look for this bottleneck?

Thanks

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7 Replies
mcowger
Immortal
Immortal

They must have different settings in the VM on IOmeter or the OS.  block size especially can do this.

--Matt VCDX #52 blog.cowger.us
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BradI100
Enthusiast
Enthusiast

I ran the same IOmeter tests on both.  But how can I check the block size on my OSs?

Thanks

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thecakeisalie
Enthusiast
Enthusiast

If you didn't specify a non-default size when you formatted them, this KB should explain: http://support.microsoft.com/kb/140365

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BradI100
Enthusiast
Enthusiast

Thanks.  These are all NTFS formatted drives.  So I guess 4 KB.

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rickardnobel
Champion
Champion

Do you test against the system disk or another "clean" vmdk? What kind of performance do you get if just copying some files inside the XP (doing reads and writes)?

My VMware blog: www.rickardnobel.se
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BenConrad
Expert
Expert

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BradI100
Enthusiast
Enthusiast

Thanks for the replies.  It looks like it was an unrelated firmware error.  I contacted the company (Drobo) and they sent a pre-release firmware that has improved performance significantly.

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