I just had a NetAPP rep telling me how good the Host Tools are getting for ESX. Those are two great utilities, thanks for pointing them out!
However, if you look at how they work, they're just automating the same process. The mbralign requires the VM be powered off. It also describes how it works:
mbralign - This is a tool the provides you with the ability to align a GuestOS's partitions in 4) steps: 1) Shut down the VM 2) Run mbralign 3) Power on the VM 4) Remove the backup file. As you can see above, prior to going thru the process, the tool, makes a backup of the .vmdk and *-flat.vmdk files, creates a new file descriptor .vmdk and properly aligned *-flat.vmdk and copies the data from the old source vmdk to the new destination vmdk. After the process is done you can manually clean up the two backup files created initially.
and a caveat:
There are 2 versions of the mbralign utility. The earlier version (1.2) has does not support multiple partitions. The 1.4 release supports Extended Boot Records (i.e multiple partitions). Mbralign was not included in the Host Utilities Kit (HUK) as it is currently, undergoing extensive QA testing simply because it modifies data and scheduling has prevented engineering from including in the kit.
Definitely very cool since you can skip the step of mounting the disk into another OS for the partitioning process. However, it might be a few revs from full production use (no support for extended boot records in the shipped HUK).
I think my first question for someone who knows more about low level file operations is what happens if you move sectors around on a VM snapshot, then revert it. Will there be any problem from the OS in accessing file descriptors that might potentially be on a different sector from when they were first opened? Assuming the answer is no, then I don't see why you couldn't replace SVMotions copy operation with something like mbralign. I don't think you'll be able to do that with the VMware APIs (you'd have to modify SVMotion source I think).
Of course, you could probably create a script or tool to do these for a VM that is powered off pretty easily.
I love the NetAPP tool though, excited to see them mature a little (having it fully tested and supporting extended boot records would be great). I'm usually building new environments these days and disk alignment is a best practice, but mbralign would save some time when you do have to re-align a VM that is having disk performance issues.
I'd be interested to see if anyone else with more experience with disks had some input.
Reuben Stump | http://www.virtuin.com | @ReubenStump
