When upgrading to vSphere 5.0, it is possible to simply upgrade datastores to VMFS5 without any downtime. It is an online and non-disruptive upgrade operation. However, there are some negatives to upgrading the datastores instead of deleting and re-creating, such as:

  • VMFS-5 upgraded from VMFS-3 continues to use the previous file block size which may be larger than the unified 1MB file block size.
  • VMFS-5 upgraded from VMFS-3 continues to use 64KB sub-blocks and not new 8K sub-blocks.
  • VMFS-5 upgraded from VMFS-3 continues to have a file limit of 30720 rather than new file limit of > 100000 for newly created VMFS-5.
  • VMFS-5 upgraded from VMFS-3 continues to use MBR (Master Boot Record) partition type; when the VMFS-5 volume is grown above 2TB, it automatically & seamlessly switches from MBR to GPT (GUID Partition Table) with no impact to the running VMs.
  • VMFS-5 upgraded from VMFS-3 continue to have its partition starting on sector 128; newly created VMFS5 partitions will have their partition starting at sector 2048.
Note the bolded item above pertaining to block size. This is important because using different block sizes will cause performance degradation when performing a Storage vMotion (Source: http://communities.vmware.com/people/Paule83/blog/2011/02/24/blocksize-matters).

 

From To Duration in minutes
FC datastore 1MB blocksize FATA datastore 4MB blocksize 08:01
FATA datastore 4MB blocksize FC datastore 1MB blocksize 12:49
FC datastore 4MB blocksize FATA datastore 4MB blocksize 02:36
FATA datastore 4MB blocksize FC datastore 4MB blocksize 02:24
With the implementation of Storage DRS, this is a big deal and is a great reason for starting fresh. However, another reason is to help ensure the datastores are clean; we’ve seen plenty of datastores with leftover dead files from previous Storage vMotions (Note: it is worth using a tool like RVTools to keep an eye on this in general, as well).

For our datastores, we’ve chosen to utilize Storage DRS to put the datastores into Maintenance Mode then delete and recreate the datastores. It’s certainly more time consuming, but the benefits are worth it.