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11-20-2012 05:26 PM - edited 11-20-2012 05:30 PM
11-20-2012 05:26 PM - edited 11-20-2012 05:30 PM
slow read speeds
Been battling this for over a year.. Read speeds are about 25% of write performance on any given day. I can write files to NSM volumes at ~100MB/S, but only read at about 15-30MB/S.
Environment:
4xP4300G2 cluster
Procurve 3400CL switches
VSA experiment:
I created a VSA on a vmware host with 2x10K SAS drives in its own cluster and the same network as the production, and was watching the total cluster throughput metric in the CMC. I was reading data from a test volume on the VSA at 90-100MB/S. During this time the total cluster throughput metric matched the read performance I was seeing on the volume.
I took the same files and copied them to a volume on my P4300G2 cluster, and read the files. Read rate was approximately 20MB/S, and the CMC cluster throughput metric never peaked above 50MB/S.
Crystal Disk Mark and I\O meter show very similar results to this test as well.
Testing in both cases was done from a physical standalone server, so it was not a case that the VSA was on the same internal vmware switch as the system reading the volume.
Flow Control\Bonding experiment:
This led me to believe the issue was related to networking transmit from the P4300G2 NSMs since a VSA on the same network performed better than the entire cluster. I tried disabling flow control on each NSM, which made no difference, then disabled ALB and used a single NIC on each P4300G2 which also made no difference.
I graph all of the iSCSI Switches with Cacti, and the network is no where near saturated. iperf tests between the NSMs (hidden feature of the CLIQ interface) report 800-900mbps throughput between NSMs in both directions.
The big things I cannot understand:
1) why 2x10K drives can outperform an entire P4300G2 cluster for Read operations when running through a VSA
2) Why writes are 2-4 times as fast as reads, especially considering these devices use RAID5.
Any ideas?
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11-21-2012 01:10 AM
11-21-2012 01:10 AM
Re: slow read speeds
How about errors/drops on network interfaces? Cacti can make graphs for these too.
Gediminas