there is a new release version 3.0:
http://www.gluster.com/community/documentation/index.php/Gluster_Storage_Platform
has anyone tried this for VM storage?
how does this compare to any ZFS based storage solution like Nexenta etc in terms of performance, usability etc?
The main goal of GlusterFS is a distributed file system, ZFS can not be distributed across a two or more servers however it's much more powerful as a local file system.
So don't try to compare them, what to use - depends on the structure you wanna build. I.e. if you are going to backup your VMs using some 3rd party tools, you probably don't need a snapshots - the most powerful feature of ZFS, if you have a large amount of drives, using zfs raidz or mirrors is much better than building md raid or using a hardware cards etc.
btw Nexenta also has some (proprietary) file system replication.
Gluster can help you implement some very cheap storage solutions in which every node is both a compute node and a storage node.
With Nexenta you are looking more at a NAS type architecture, which means an additional server which becomes a single point of failure unless you build a storage cluster.
With Gluster you can build a huge distributed file system very cheaply. It's great for HA.
ZFS/Nexenta has a lot of great features that you don't get with Gluster. Data-deduplication and features that detect "silent" data corruption come to mind.
If you want to go cheap go Gluster. If you want something that is cheap compared to Netapp go Nexenta.
I build NexentaStor based storage platforms for a living so I'm biased here but I would go with Nexenta. For scale take a look at http://www.informationweek.com/news/software/open_source/showArticle.jhtml?articleID=227600191&subSection=Hosted+Software - ultimately this will be about 1PB all off NexentaStor.
If you want to start small and expand then take a look at http://www.va-technologies.com/sbb
With VMDC you can link VMWare, XenServer and Hyper-V all into the storage and create machines direct from storage platform, much quicker.
Windows performance is great, CIFS, NFS etc. Integration to AcivteDirectory etc.
If you're in the UK do take a look at the link above.