Performance reading from or writing to a Dell Equallogic SAN over iSCSI is very slow in ESX(i) 4.0 and later. Read speeds from an ESX Service Console and/or write speeds to an iSCSI-initiated Repository LUN are correspondingly slow when the configuration of the SAN seems to be fine.
The firmware on the Equallogic SAN may well be out-of-date. To take advantage of several ESX(i) 4.x and later features in VMware, the Equallogic Storage Array's firmware must be upgraded to version 5.x or later.
http://en.community.dell.com/techcenter/storage/w/wiki/2687.aspx
Read the above regarding the new features (hardware accelleration, vStorage API support, many others). Download and upgrade your Equallogic Arrays to a firmware revision of 5.x or later.
