You are very welcome. If you haven't done so already, install SANHQ in your environment. It will help you monitor your array. This will help you monitor performance per volume and overall.
IOPs depends on the type and size of your IOs. Larger IO sizes yield fewer IOs/sec but greater MB/sec. The reverse is also true. Lastly how random vs. sequential your IO is will have an impact as well.
Keeping heavy IO VMs on different volumes is recommended as well.
Depending on when you are going live, I would suggest upgrading to firmware 5.2.0. Which is currently in Early Production Access but will be GA'd soon. It has a number of important fixes that make it a very worthwhile upgrade. These are detailed in the fix list on the EQL support website.
Lastly if you are doing applications like SQL or Exchange, I would recommend using the MS iSCSI initiator to connect to those data/log volumes. This will allow you to install the HIT kit which will integrate snapshots (and replication) seamlessly into those applications.
What kind of switches are you using? If they are not stacked make sure you have at least 3x GbE interfaces trunked between them. Flowcontrol needs to be enabled on server and array ports. Along with spanning tree portfast. If you are using Jumbo Frames, don't use VLAN 1 (default vlan) on your switches. Create a separate VLAN instead.
Finally, make sure you have the lastest build of ESX v4.1. There are updated drivers that customers on the VMware forums indicate reduce latency.
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