Can a single Guest VM use multiple VMFS Datastores?

[neilchapman]

I was trying to think of the best way to ask this question.

Can a single Guest VM use multiple VMFS Datastores?  One Datastore for the C:\OS drive, one Datastore for the D:\App drive, one Datastore for the E:\Data drive? 

I know the logical question would be "Why would you want to?", in we have a scenario where it is necessary.

[Troy_Clavell]

Yes, this is possible.  A good use case for spitting up your data is maybe a database server, where you data drive may need higher IOPs

[neilchapman]

Are there any caveats?  We're planning on doing this with DAS. 

N

[eeg3]

A minor caveat would be that your VM would then rely on two groups of storage to be available.

[neilchapman]

Understood.  Reliance on multiple datastores to be available.

I guess my "caveat" question was more specifically related to DAS.  Drives internal to the Host utilizating a RAID controller should be no problem, correct?  We're not doing RDM in this scenario, right?  This is strictly multiple hardware arrays presented to vSphere; then created as VMFS Datastores; then those multiple VMFS Datastores presented to a single VM Guest machine.

I just wanted to ensure I thought this through correctly before purchasing the hardware.

Please let me know if there is a flaw in my logic.

Thanks!

[schepp]

I would say this is common practice. We split almost all of our server VMs and seperate the OS discs from the user data discs.

As an example: our e-mail server.

OS on fast RAID A,

A few hundred GB of Inboxes on fast RAID B,

Multiple TB of IMAP folders on slower SATA RAID C.

Only thing to worry would be the connectivity of those different storages I'd say. If you use iSCSI NAS systems for example, every new switch will add a point of failure. But since you want to use DAS, that shoudln't be a problem

edit:

problem with DAS is loosing some flexibility. As soon as you get more then just one ESXi host, you want to use a shared storage to benefit from features like vMotion, etc. ( vSphere 5.1 comes with enhanced vMotion, and weakens my arguments )

Also relying on a single internal RAID controller is something I would not do in bigger productive environments.

Regards

[eeg3]

I presume you're aware that you can't use HA/DRS/etc with local datastores, but using them is not a problem as long as they're on the hardware compatability list.

[neilchapman]

Yes, understand HA issues with DAS.  Understand there is an migration path when more $$ available. 

My question originated because all documentation discusses why VMFS is great for multiple guest VMs to share.  The opposite discussion (single guest with multiple datastores) is dominated with information about using Raw Device Mappings - and those supported solutions only use FC or iSCSI SAN's because of LUN mappings.  I found no information about using multiple DAS Datastores a single Guest VM.  I just wasn't sure how/if it was done. I figured there probably wasn't documentation becasue it's obvious to most folks.  I didn't want to order hardware and then find out we couldn't do what we planned.

Does anyone know where I could find documentation about this question - presenting multiple datastores to a guest vm for use as seperate logical drives?

N

[a_p_]

I figured there probably wasn't documentation becasue it's obvious to most folks

That's probably why.

You can certainly have multiple datastores no matter whether thy are on local storage or shared storage and place a VM's virtual disks on the datastore you want. Please remember that only a single datastore is supported on a LUN (i.e. no partitioning of LUNs).

In case this is important for you regarding disk space. As of ESXi 5.x VMware change the default location for snapshots. Before ESXi 5.x the snapshots for all virtual disk - regardless of their location - were stored in the VM's base folder. With ESXi 5.x the default location for each virtual disk is the folder of it's parent virtual disk.

André