Slow Write speed on Linux VM

Linux team raised issue that 3 VM's are reporting very slow write speed, write speed as low as 10 MB/s, where as other linux VMs with exactly same configuration on same host are writing data at 240 MB/s.

All VM are on same esx host , I tried to move them around on different hosts but same result. ESX are 5.0 & Storage is IBM SAN.

Thanks

Ajay