SQL on RDM/Passthrough disks?

Whether you are using VMWare or HyperV in your environment, what are the factors that make your decision on using or not using RDM / Passthrough disks?

I ask because in an environment I'm working in, I have been tasked to set up a HyperV cluster and 5 virtuals. One virtual houses the clients main app and SQL 2008. We were asked by the vendor to use a separate LUN, allocated to 64k block, and passthrough disk. I was told however the SAN should be fast enough, just put everything on one giant LUN.

LUN = 2.6 TB,
Users = 60 more or less.
Switch is a Gigabit HP 2510G
Virtualization = HyperV
2 Node Cluster / Cluster Shared Volumes

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dave330i

Don't know about Hyper-V, but in VMware if you're setting up SQL cluster you have to use RDM.

blargoe

In my experience, application vendors are FOS and often request hardware specs that are largely overkill. Unless they say they won't support you unless you use a passthrough disk, I wouldn't (if it limits the manageability of the VM like it does in some aspects in VMware... not sure what restrictions are in place in HyperV). You can still give the database disk its own lun by dedicating a LUN to the VHD file on which the database files are located (and set the 64k allocation, etc)

it_consultant

langenoir wrote: »

Whether you are using VMWare or HyperV in your environment, what are the factors that make your decision on using or not using RDM / Passthrough disks?

I ask because in an environment I'm working in, I have been tasked to set up a HyperV cluster and 5 virtuals. One virtual houses the clients main app and SQL 2008. We were asked by the vendor to use a separate LUN, allocated to 64k block, and passthrough disk. I was told however the SAN should be fast enough, just put everything on one giant LUN.

LUN = 2.6 TB,
Users = 60 more or less.
Switch is a Gigabit HP 2510G
Virtualization = HyperV
2 Node Cluster / Cluster Shared Volumes

We are a clustered Hyper-V shop and I will only support a pass through disk if they NEED the disk mounted in the VM to be larger than 2 TB. Once we implement server 2012, I will not support pass through disks. Clustered hyper-v with pass throughs is nasty.

This is apropos because I was, just now, reading the Commvault Simpana 9 manual where it was telling me I couldn't do a VHD level backup if the machine had pass through disks.

Bottom line, Microsoft supports SQL on Hyper-V - your vendor should as well.

I assume that you are on a 4/8GB FC SAN or 10GB iSCSI?

langenoir

it_consultant wrote: »

I assume that you are on a 4/8GB FC SAN or 10GB iSCSI?

We are using 1 Gigabit iSCSI connection.

jmritenour

I've seen and supported plenty of both. Generally speaking, I'd rather see everything that is virtual, stay 100% virtual. Though RDMs definitely have their place - ie, you're connecting a LUN from an existing physical instance, or certain clustering scenarios, or need a drive larger than 2TB.

it_consultant

langenoir wrote: »

We are using 1 Gigabit iSCSI connection.

That is going to be more of a performance problem than VHD vs pass through. I recommend biting the bullet and going to 10GB iSCSI or 8 GB FC depending on what your SAN supports. I would not put any type of database application (Exchange, SQL, etc) where the disk was being accessed over a 1GB connection.