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We experience a slow read performance with a high read latency in vSphere/ESXi on our Equallogic iSCSI array (14x 750gb in RAID10). We checked already very much but cannot find anything.



2x 1gig intel 85276 connected to a dell 5524 with Jumbo frames on and flow control off.

Equallogic connect to the Dell 5524 switch, with jumbos on.

Everything is running on default VLAN1, we still need to create a sepearate vlan for the equallogic and host.

Our vmK setup:

ESXi vmKernel setup

Our benchmarks with atto in a Windows VM:


Write performance is without multipath and with multipath fine, it does perform well. But read is terrible slow.

Does anyone know where we can search to fix this?


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RAID is OK, not rebuilding? Do you have any stats from the SANHQ? IOPs etc, there's also a "load level" indicator there. Watch it during the benchmarks. – 3molo Apr 18 '12 at 13:34
At the moment we do not have SANHQ running cause we've got this EQL unit for test purposes. We do not have to correct equallogic support account and can't download it yet. The unit is not rebuilding or anything else, the write is also great. The latencies for write a 2 or 3, but read is always higher then 10+ ms with one VM on the unit.. – Tom Apr 18 '12 at 13:35
Obviously not the ESXi host or the network, your writes are fast, so there must be a problem with device settings, read cache maybe? – Tim Apr 18 '12 at 13:50
Equallogic does what i know only have write cache, the controller is running in write back at the moment. There are 12 active disks, the speed of the read should be at least as fast as one sata disk(+- 80mb/sec), right? The connection is also OK, because the write is getting along the 1gbit. Should this be the fix?‌​43320 We are still running on VLAN1 which maybe doesn't handle jumbo frames correctly. – Tom Apr 18 '12 at 13:57
tried dropping all the MPIO stuff and connecting just a single vmKernel port with a single physical adapter attached to a single controller of the Equallogic SAN? – the-wabbit Apr 18 '12 at 15:25

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