Welcome to the first in a series of posts related to new storage enhancements in vSphere 5.1. The first of these posts will concentrate on VMFS. There are two major enhancements to VMFS-5 in the vSphere 5.1 release.
VMFS File Sharing Limits Increase
Prior to vSphere 5.1, the maximum number of ESXi hosts which could share a read-only file on a VMFS filesystem was 8. This was a limiting factor for those products and features which used linked clones. Linked Clones are simply “read/write” snapshots of a “master or parent” desktop image. In particular, it was a limitation for vCloud Director deployments using linked clones for Fast Provisioning of vApps and VMware View VDI deployments using linked clones for desktops.
In vSphere 5.1, we are increasing this maximum number of hosts that can share a read-only file (or to state this another way, we are increasing the number of concurrent host locks) to 32. This will only apply to hosts running vSphere 5.1 and higher on VMFS-5. Now vCloud Director and VMware View deployments using linked clones can have 32 hosts sharing the same base disk image.
This makes VMFS-5 datastores as scalable as NFS for VDI deployments using VMware View and vCloud Director deployments when using linked clones.
It should be noted that versions of VMware View 5.0 (and earlier) limited the number of hosts which could use linked-clone based desktops to 8. This was true for both VMFS and NFS datastores. VMware View 5.1, released earlier in 2012, increased this host count to 32 for NFS on vSphere 5.0. With the next release of VMware View & vSphere 5.1, you can have 32 hosts sharing the same base disk with both NFS & VMFS datastores.
One final point – this is a driver only enhancement. There are no on-disk changes required on the VMFS-5 volume to benefit from this new feature. Therefore customers who are already on vSphere 5.0 and VMFS-5 need only move to vSphere 5.1. There is no upgrade or change required to their already existing VMFS-5 datastores.
VOMA – vSphere On-disk Metadata Analyzer
VOMA is a new customer facing metadata consistency checker tool, which is run from the CLI of ESXi 5.1 hosts. It checks both the Logical Volume Manager (LVM) and VMFS for issues. It works on both VMFS-3 & VMFS-5 datastores. It runs in a check-only (read-only) mode and will not change any of the metadata. 
If you find yourself in the unfortunately position that you suspect that you may have data corruption on your VMFS volume, prepare to do a restore from backup, or look to engage with a 3rd party data recovery organization if you do not have backups. VMware support will be able to help in diagnosing the severity of any suspected corruption issues, but they are under no obligation to recover your data.
I’m sure you will agree that this is indeed a very nice tool to have at your disposal.
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