While walking over the solution exchange, my eyes got distracted by a company called Gluster. Roughly speaking they are offering an affordable storage solution that can be build up from basic industry standard x64 components.
Gluster is an open source NAS that can be setup using linux servers. It is an aggregated NFS filesystem that offers a single mount point for multiple storage nodes. For creating a VMware storage there are basically two components, the -open source- GlusterFS file system and the -proprietary- VMStor addon.
This appears to offer all the main features one would expect from a storage solution. High Availability is offered via node replication. Storage backend snapshots can be used and are fully integrated into the vSphere Client. Dynamic scaling of the volume is possible by adding or removing storage nodes on the fly which in effect allows you to grow or shrink the single storage volume. There’s also the possibility to backup your VM’s using scripts to a Disaster Recovery site. Virtualisation, hardware is abstracted by offering all the nodes into a single volume.
The Gluster file system component is run from user space and builds the volume up on top of the native filesystem (for example ext3 or zfs). This way you could even use excess space from existing servers. The way the file system is presented to your VMware host is by presenting it as a NFS fileserver.
The VMStor addon takes care of VMware specific features, such as making sure that a virtual machine is completely stored on one node and does not end up scattered over multiple nodes. This helps to improve security in case of a node failure. VMstor is also the part that offers the storage server backed snapshots and the one click backup feature.
It looked like a really interested product to me personally, but as I have no hands on experience myself, it is probably best to have a look at their web site for all the specific details.