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7 Replies Last post: Nov 23, 2009 5:03 AM by Bjoern.Gies

Shared SCSI Volume posted: Nov 20, 2009 2:57 AM

Bjoern.Gies

11 posts since
Oct 10, 2007

Hello VMTN community,

I got two SuperMicro servers, each with an Adaptec 29320ALP-R[1] U320 parallel SCSI controller connected to the same external RAID system.
The RAID system is an EUROstor ES-6600[2] with two U320 channels.
I'm running ESXi 3.5 on both systems, seperated to each other.

The EUROstor RAID system offers the possibility to propagate a RAID volume to both channels - for clustering as they say.
I wonder if the ESXi can handle such a shared volume or if there will be problems when both are accessing the volume. I thought about having some virtual machines stored on that volume but only registered/mounted in one inventory of the two ESXi at a time to reduce possible conflicts. So that I can easily run the virtual machine on the other host, maybe when one physical server fails.

To illustrate it a bit:
RAID system
   System-Volume-1
      Host1 only (SCSI Channel 0; ID 0; LUN 0)
   System-Volume-2
      Host 2 only (SCSI Channel 1; ID 0; LUN 0)
   VM-Volume-1
      Host1 only (SCSI Channel 0; ID 1; LUN 0)
   VM-Volume-2
      Host2 only (SCSI Channel 1; ID 1; LUN 0)
   Shared-Volume
      Host1 & Host2 (SCSI Channel 1&2; ID 2; LUN 0)

I found alot about shared SCSI disks for virtual machines, but not for ESX(i) itself. Found something about "cluster aware" OS, but most of them talked about SAN.

Thanks for any help or tipps, links whatever that might help me on that topic in advance!

Greetings from Germany

Björn

[1] http://www.adaptec.com/en-US/products/Controllers/Hardware/scsi/entry/ASC-29320ALP-R/
[2] http://eurostor.de/german/ES6600U.D.php

Tags: 3.5i, scsi, shared, disk

Re: Shared SCSI Volume

1. Nov 20, 2009 6:18 AM

in response to: Bjoern.Gies

DSTAVERT

3,520 posts since
Nov 30, 2003

It is possible. Some cluster type arrays by HP and Dell do support it. VMFS, the ESX(i) filesystem, is a cluster type filesystem. ESX(i) will keep you from starting a machine on two hosts simultaneously. If you have had success please do a more thorough report. I am sure there would be interest.

Re: Shared SCSI Volume

2. Nov 20, 2009 6:54 AM

in response to: DSTAVERT

Bjoern.Gies

11 posts since
Oct 10, 2007

Hi DSTAVERT,

thanks, so it's worth a try.
Gonna check that next week.

Greetings

Björn

Re: Shared SCSI Volume

3. Nov 20, 2009 7:32 AM

in response to: Bjoern.Gies

Texiwill

10,432 posts since
Jan 13, 2004

Hello,

Unless the Array has a SAN like controller ala HP MSA 500, then this type of configuration will not work as there is nothing controlling the locks required by ESX. Dell does have a similar device.

However, 'Disk Trays' will not work. They work for MSCS as MSCS handles the lock 'communication' via a private network.

Best regards,
Edward L. Haletky VMware Communities User Moderator, VMware vExpert 2009
Virtualization Practice Analyst
Now Available: 'VMware vSphere(TM) and Virtual Infrastructure Security'
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Re: Shared SCSI Volume

4. Nov 20, 2009 8:20 AM

in response to: Bjoern.Gies

savantsingh

79 posts since
Oct 2, 2008

The ESX would add a lock to the VM when it is in use. Regarding the "cluster aware" volumes you are not running a Virtual Center server so ESX hosts are not in a cluster. In other words the storage is not shared on a VC cluster level.

Having said that i agree with Texiwill unless the array controller supports shared LUNs it wouldn't work.

But it will nice to know the results if you can test sharing the volume datastore (shared volume) on both hosts. I would assume if you try and power on the VM already in use on the other host you would get an error saying " cannot open file or something" cause of the lock.

If you found this information useful, please consider awarding points for "Correct" or "Helpful".

Re: Shared SCSI Volume

5. Nov 20, 2009 8:52 AM

in response to: Texiwill

DSTAVERT

3,520 posts since
Nov 30, 2003

Björn
I took it that you had already done it. As Edward says unless the array device has SAN type controller you would be out of luck. If you use the array attached to another server and added a software package to provide either iSCSI or NFS you would be able to share the storage.

Re: Shared SCSI Volume

6. Nov 23, 2009 12:16 AM

in response to: savantsingh

Bjoern.Gies

11 posts since
Oct 10, 2007

Hello all together,

thanks for all your answers. I gave it a try this morning.
A quick overview what I've done and the results:

Booting both servers with the shared volume [ Success: Servers are booting ]
Creating VMFS on the shared volume through Host#1 via VI Client [ Success: Datastore added ]
LVM.EnableResignature set to '1' on Host#2 [ Success: Just created VMFS showing up ]
Creating new VM on the shared volume through Host#1 [ Success: VM created and booting (up to BIOS - no OS installed) ]
Registering the VM on Host#2 [ Success: VM registered - shown as powered off ]
Powering on the VM through Host#2 [ Failed: "Could not power on VM : No swap file." \ "Failed to power on VM" ]
Powering off the VM through Host#1 [ Success ]
Starting the VM through Host#2 again [ Success: "Virtual Machine Message" \ "msg.uuid.moved"(1) -> Choosing Keep, Booting afterwards ]

Not looking that bad - for a simple FailOver. Gonna play a little bit more and report if theres anything important.

Notes:

The just created VM is showing up instantly when browsing the datastore through the other host
Free disk space of the volume isn't updated on the host when creating a VM through the other host on the shared volume
Paths to mounted ISOs are broken on the other host (of course)

Greetings

Björn

(1) http://professionalvmware.com/wp-content/uploads/2009/01/image1.png (Same message - not my screenshot)

Re: Shared SCSI Volume

7. Nov 23, 2009 5:03 AM

in response to: Bjoern.Gies

Bjoern.Gies

11 posts since
Oct 10, 2007

Hi again,

I just tried what's happening when i suddenly turn off Host#1 where the VM on the shared volume is running. To my surprise I was able to start the VM on Host#2 without any problem - except the msg.uuid.moved message. Didn't expect the whole "thing" to be that robust.
Of course there was/is luck the filesystem inside the VM isn't wasted.

Greetings

Björn

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