Shared R/W disk for multiple VMs

[sutcliff]

IBM has a product called GPFS. Using GPFS you can create a filesystem on a lun that allows multiple Red Hat Operating systems to do read and writes. It locks down at the file level. You cannot write to the same file. Just the same filesystem.

There is no controlling host like NFS. The multiple OS' are writing directly to the shared file system.

Is there anything like that for VMWare that will still allow a Vmotion?

I need a way to have multiple operating systems read / write to the same filesystem and still be able to do vmotion.

Thanks,

Brian

[mcowger]

You CAN share a disk between VMs - both VMDKs and RDMs - we've played with things like GFS and QFS and they are fine.

--Matt

[dmorgan]

As Matt pointed out here, this functionality is already built into VMWare.

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[sutcliff]

How do I do that? Do go into edit settings, add, hard disk, use an existing disk?

Thanks,

Brian

[mcowger]

Exactly, as well as setting the scsi bus options for sharing.

[sutcliff]

I could not power on the VM after I did this. I received a error that the disk needs to be created in thick mode.

I call VMWare technical support and showed this post to them. They say this is not supported.

Any idea what thick or thin disks means?

Brian

[Texiwill]

Hello,

You are trying to create a shared disk cluster, ESX v3.5 does not currently support this. The documentation for MSCS covers what you need to do to create any shared disk cluster whether it is using RedHat or VMware. The main ingredient is the use of an RDM for the shared drives not a VMDK. Also, it may be necessary to place the boot drives on local storage not necessarily remote storage. However, the virtual hardware creation steps listed in the MSCS documentation apply to any shared disk cluster technology.

Best regards,

Edward L. Haletky

VMware Communities User Moderator

====

Author of the book 'VMWare ESX Server in the Enterprise: Planning and Securing Virtualization Servers', Copyright 2008 Pearson Education. As well as the Virtualization Wiki at http://www.astroarch.com/wiki/index.php/Virtualization

[Wimo]

Thick disk: Create the disk from SC with vmkfstools.

vmkfstools -c 10G -d thick diskname.vmdk

I don't know the difference between that and leaving out the switch, which would create a disk which, to my way of thinking, is thick too. As opposed to thin, where it only uses up as much space as the data on the drive. But I got the same error first time I did what you are doing (more or less).

[sutcliff]

I read that:

VMotion does not currently support the migration of clustered

applications or raw or undoable virtual disks. If you have clustered

applications or raw or undoable disks, store the disks on separate VMFS

volumes from the virtual machines you plan to migrate using VMotion.

Does this mean that a RDM disk will not work for vmotion?

Thanks,

Brian

[Texiwill]

Hello,

Review the information for http://www.vmware.com/pdf/vi3_301_201_mscs.pdf, also not that you must be using ESX v3.0.x not v3.5 as clustering does not currently work with 3.5....

As for vMotion of clustered disks raw or otherwise, since most boot volumes should be on local storage (per above guide) those disks can not be used with vMotion. Also since the RDM is tied to two virtual machines instead of one, vMotion would have some troubles hooking it back up to two different servers. MSCS/RedHat Clusters or any other shared disk cluster has some very specific rules for setting up hardware. On page 37 of these guide are specific steps for the location of VMDKs for the data stores.

As for vMotion, if the cluster is properly setup (per the guide) vMotion can not be used due to the limitations on the placement of VMDKs. Hence the statement you have read.

Best regards,

Edward L. Haletky

VMware Communities User Moderator

====

Author of the book 'VMWare ESX Server in the Enterprise: Planning and Securing Virtualization Servers', Copyright 2008 Pearson Education. As well as the Virtualization Wiki at http://www.astroarch.com/wiki/index.php/Virtualization