I would suggest breaking up the TB volumes into smaller ones. I.e. 600GB  (depending on the size and number of the VMs on each datastore)   Each volume has a defined queue, typically 32.   More volumes mean more outstanding IOs can be running.   Also there are times when ESX must lock (reserve) a volume, while reserved no other node can do IO to that volume.  So more volumes lessens the issue and means other volumes will still have ongoing IOs.  Here are some best practices 1.)  Delayed ACK DISABLED 2.)  Large Receive Offload DISABLED 3.)  Make sure they are using either VMware Round Robin (with IOs per path changed to 3), or preferably MEM 1.1.0. 4.)  If they have multiple VMDKs (or RDMs) in their VM, each of them (up to 4) needs its own Virtual SCSI adapter. 5.)  Update to latest build of ESX, to get latest NIC drivers.   6.)  Too few volumes for the number of VMs they have. Here's some source material for the Delayed ACK kb.vmware.com/.../search.do virtualgeek.typepad.com/.../a-multivendor-post-on-using-iscsi-with-vmware-vsphere.html How to disable LRO Solution Title HOWTO: Disable Large Receive Offload (LRO) in ESX v4/v5 Solution Details Within VMware, the following command will query the current LRO value. # esxcfg-advcfg -g /Net/TcpipDefLROEnabled To set the LRO value to zero (disabled): # esxcfg-advcfg -s 0 /Net/TcpipDefLROEnabled NOTE: a server reboot is required. Info on changing LRO in the Guest network. docwiki.cisco.com/.../Disable_LRO How to add virtual SCSI adapter:  kb.vmware.com/.../search.do
Hello all we have just bought a PS4100X with 12 x 600GB 10K SAS (7.2TB RAW) This device is due to replace our existing MD3000I Powervault Device that is being used in out Vmware ESX enviroment. What RAID / ESX  Datastore configuration would people recommend. Currnently we have the following set up for example. 2 x Raid 10 Disk Groups with 1TB Virtual Disks on each. The 2 1TB Disks are then presented to ESX and used by 2 Datastores. cheers in advance.
PS4100X - Initial Set configuration (vSphere 5)