How to storage Migrate RDM to RDM

[abugeja]

Hi,

We are moving storage arrays for an environment where physical RDMs are used. Normal VMFS volumes are easy to migrate but what's the best practise to storage migrate RDM disks for Window servers? RDM's are required for SQL backups

Thanks

[continuum]

RDMs are links to a device in /dev/disks/
So if you want to migrate an existing RDM to a new disk or LUN available to the same esxi host you can clone device to device with dd (this only works if target device is same size as source device or larger)
You would run a command like
dd if=/dev/disks/source-device bs=1M conv=notrunc of=/dev/disks/target-device
If you want to reduce the size along the way this approach will not work.
Instead you would use a Windows VM which has connect both target RDM and source RDM and would use robocopy or similar tools to copy over the content.

[abugeja]

robocopy was my first thought for this piece of work.

I wonder if the storage array could perform a copy between the old and new RDM  then we just reattach it

[continuum]

The content of your RDMs will make a big difference.
If the RDM is filled with lots of small files robocopy will be quite slow.
On the other hand robocopy may be the fastest option if you have the RDM only partially filed or have it filled with large files.

[Sreejesh_D]

yes, you can create the new lun as clone from the old lun at storage level. It will be a faster solution since they copy is done at the storage level. Most of the modern storages have snapshot and clone features.

One the new LUN created you can unmount the old RDM and create new RDM with the new LUN. You can see all data copied with the same volume label.

[abugeja]

Thanks I would of thought this would be possible as well. Ill reach out to our storage vendors regarding this.