Whats the cause of VMWare esxi Ubuntu very slow disk performance (3MB/s)?

Currently I am running Zentyal Server(Ubuntu) as Guest on a esxi 5 host on a Adaptec raid controller RAID 10 with Enterprise WD hard drives, 8 Core CPU and 8 Gb of ram (I know a bit overkill) to server about 40 Users. Currently 300GB of storage is being used out of 800GB on Thin Provision.

At the start Read/Write Performance was amazing (200MB/s read, 170MB/s write) but as the storage grow performance has come down to 9MB/s read and about 2-3MB/s write using dd and hdparm.

Cannot understand what could cause this, Any help would be appreciated. I have checked CPU and not much of it is being used unless someone is writing to it(maxes out, no antivirus on the server).

This seems to only happen on this Guest as I tried to create another Guest and hdparm and dd returned average 200MBs/170MBs read/write performance.

I have found the solution to this problem:

• Installing VMware Tools on the Ubuntu guest increased the performance a little.
• The performance was significantly reduced due to the fact that I had assigned the Guest 4 virtual Sockets (vCPUs), following some research I found out that this causes big problems with Ubuntu (Possibly Linux) operating systems and causes longs switches and delays in the system responsiveness. After taking down the Virtual Sockets to 1 the OS performances hit it's peak performance instantly after a restart.

New Readings:

• Using hdparm: -- Average Cached reads: 13255 MB/sec -- Average Buffered disk reads: 146 MB/sec

• Using dd: -- Average write speed(bs=16k, count=256k): 169MB/sec

I do know that write speed shouldn't be higher than read speed but as we all know dd is not as accurate as it should be! But still a big increase from the pathetic average speed of 9MB/sec read and 3 MB/sec write.

Hope this helps those who have this issue.