Hello, Sorry I was not able to get back to this post right away. I have installed the latest version of the software 5.8.xxxx Regardless that did not help. I faced the same issue. I was looking on the internet recently and came across some recommendations for speeding up VM's performance. So as per ...

yes 5.4.0 (build 20100708) , are there any known issues with that revision?

In reference to read performance I have based my findings on HDtune not ATTO. HDtune can run write bench marks concurrently from 3 VMs without issue. Its when I run HDtune read bench when it drags all the 3 VMs down. ATTO runs Read Write tests at the same time therefore, we may not notice these perf...

https://www.dropbox.com/s/hv2muwhtxdoga ... of%203.bmp
https://www.dropbox.com/s/te383hvyhsyxn ... of%203.bmp
https://www.dropbox.com/s/7no83l292oky4 ... of%203.bmp

ATTO: 1 VM running no other VMs running anything:
https://www.dropbox.com/s/xrz2jspme24m4 ... hot001.bmp

HDtune: 3 VMs concurrently runing the same HDtune Read bench:
https://www.dropbox.com/s/5hmb47c4x791t ... hot002.bmp

My setup: 1 ESXi 4.1 physical box (3.2 GHz quad core i5, 16 GB ram) 1 (w2K8 r2) starwind san/vcenter physical box (3.0 GHz dual core2duo, 8 GB ram, 3 - sata2 7200 rpm disks for the vm datastore) Write through caching enabled with 64 size for the target. Hdtune reports read speeds of 250+MBps on the ...