SQL - VMFS or RDM?

[pegasus00720111]

We are looking at doing a P2V of a SQL server, all local storage.  This server has a 50GB OS partition, 100GB drive D (Data) partion and a 200GB Drive E (Backup and Logs) partition.  This server is a management server used for reporting by our Active Directory team and utilization is fairly low.  This will be our first SQL server we will be virtualizing and I'm trying to determine a best practice moving forward.  Has there been a general move towards one direction or another (VMFS or RDM) as a best practice for SQL?  I believe both have a max size of 2TB and performance between the two formats are about on par with one another.  So, for example, in our case here we were thinkiing of possibly using separate LUNs for each partition formatted as VMFS or just one large LUN and partitioned since IO would likely be low for this particular VM.  One annoyance we realize with using VMFS for dedicated LUNs for VMs, is that when you do this and dedicate the entire LUN to a vmdk file for the VM, you have a constant Data Store Usage Alarm on that datastore.  But, if you use an RDM for that VM and want to use snapshots or storage VMotion, wouldn't that cause issues as well?  I know one plus with RDM is if you are migrating a physical server to a VM and use RDM, if for some reason you need to go back to the physical server, you could remap the LUN back to the physical server.

We just would like to determine a best practice for this scenerio to move forward with, vmfs or rdm.

[idle-jam]

if you use a virtual mode of RDM you will still have a pointer vmdk in which snapshot can be created too. i would go for VMDK as in terms of performance it would be much faster being on the new hardware. here is a good read too: http://www.vmware.com/files/pdf/sql_server_virt_bp.pdf

[J1mbo]

Just use VMDKs and, if it's a 2003 server, align the partitions as part of the process to a 64KB boundary.  Go easy on vCPU allocation.

[pegasus00720111]

Thanks, but I just want to clarify further.  In our environment we will likely have many VMs with dedicated LUNs to those VMs, so just trying to determine what is the most common practice to handle this, using VMFS for dedicated VM LUNs or RDMs.  Also, if the LUNs will likely need to be expanded in the future, would it be easier to then use RDM or VMFS (with VMFS the vmdk file within the VMFS volume would also need to be expanded).  Like I mentioned before, one annoyance with using VMFS for dedicated LUNs is that when that LUN (datastore) is associated to the VM and taken up by a vmdk file (since it is soley for that VM), the Datastore Usage alarm is constantently in alert status.  There is a VMware kb article where if you try to change the alarm at the datastore level to get around this, then this could cause problems in vCenter.  This may mean haivng to live with many alerts in vCenter for datastore usage which would seem to be an annoyance.  I'm just wondering how other sites are handling assigning VMs dedicated LUNs for storage, VMFS or RDMs and if VMFS, what about the datastore being in the alarm state if given to one vmdk file?

thanks for any assistance with this,