I am using HP StorageWorks (formerly known as LeftHand) P4000 Virtual SAN Appliance (VSA) for my iSCSI storage. It is a virtual machine that uses any storage (in my case local disks) and presents it as iSCSI targets. It is enterprise level software (as opposed to OpenFiler) with such features as high availability (network RAID), thin provisioning, snapshots, replication and Site Recovery Manager plugin. The list price is 4500 EUR, but the good thing is that it can be used for free without the advanced features such are replication, snapshots, HA, etc. Those features can be used in trial mode for 60 days which is perfect for Site Recovery Manager testing. HP also sells hardware equivalents of P4000 which are basically regular computers with SAN appliance software.
The SAN appliance software is called SAN/IQ and new update version 9 was released last week. For me the most interesting new feature is vStorage API for Array Integration (VAAI). Now in vSphere ESX4.1 there are some storage related operations offload from the vmkernel to the storage processor. One of them is zeroing newly created thick disk (eager zero thick disk) needed for fault tolerance VMs. To test if VAAI works I compared creation of 10GB FT enabled disk. Without VAAI the disk was created in 249 seconds with VAAI it took only 193 seconds without any ESX host CPU overhead or unnecessary SAN traffic.
Here is the screenshot of a datastore with hardware acceleration.
I love when you can play with enterprise technology at home.
The HP VSA can be downloaded here: www.hp.com/go/tryvsa
Tom Fojta's Blog 
Thank you for the blog. If the intent of hardware acceleration is to offload ESX Vmkernel work to SAN hardware, and if an HP VSA runs as a virtual machine within the ESX host, then wouldn’t an ESX host simply be offloading work to itself?
Isn’t hardware the key to “hardware acceleration”, something that a VSA lacks?
Well, in the case of having the HP VSA on the same host as other VMs you would be right, but if you have more hosts, you really are offloading all the copying (in the case of Storage vMotion) or zero writes (in the case of Eager-zero-thick) to the VSA host. And you also free SAN network from unnecessary traffic.
Nowadays all storage hardware is just bunch of commodity disks with x86 hardware and some really smart software. So you cannot expect “hardware acceleration” similar to GPU offload. So all the storage related operations are done by that smart software for which you pay big $$$.
I love the VSAs. I have put them into many of my clients. There are lots of great videos and documents from HP regarding the initial setup, but nothing on how to add additional storage down the road to an appliance already in production. I have had to do this process twice myself in the last twelve months so I assume others are looking for this process.I wrote these articles and wanted to share them with you. Hope they help!
http://supertekboy.com/2014/01/05/how-to-add-space-to-a-hp-storevirtual-virtual-san-appliance-part-i/
http://supertekboy.com/2014/01/07/how-to-add-space-to-an-hp-storevirtual-virtual-san-appliance-part-ii/