Sharing VMDK's between VM servers

[DAckroyd]

Does anyone know if you can use the same VMDK on 2 VM's?

What I am trying to do is setup a new set of servers identical to (exept the problems) our current servers and we have a VMDK file for the old server and I was wondering if while I was setting up the new servers whether I could share the VMDK so data on the 2 servers was identical. The Servers are running Server 2003 and our hosts are VMware ESX3.5 connecting to a SAN

thanks for your help

[apaton]

You would like two different Win2003 VM's to access the same VMDK file?
This can't be done and would cause corruption any way. (NTFS is not a cluster filesystem)

In clustered environments that share virtualdisk you would have to use RDM's and not VMDK's.

Andy

[DAckroyd]

thanks, I was hoping that I could just attach the data drive but I'll just have to copy the data over when the time comes to kill the old box off

[apaton]

Keep the data synchronised between two windows boxes on a periodical basis.


I like rsync on Unix, so these windows tools may/may not help, I'm sure the Windows forum will have better answer.

DeltaCopy - Rsync for Windows


Andy

[tmcd35]

I forget the term, I think it's called a 'differencing file' where by each VM sees a read-only copy of the master VM and have their own writable file where they store their own changes (or differences) to the master VM.

I believe this feature is supported by ESX and it can be done with VMDK's. Can't remember what is called though. But yes it is actually possible to do what you want.

Each VM sees the VMDK as a unique drive to them rather than a single cluster chared volume. No data corruption occurs because the difference are written to the differencing file and not the share VMDK.

[DAckroyd]

I have the server on a septerate vSwitch to keep it from seeing the old server - havng to set up identialy and don't want to cause problems

[DAckroyd]

thanks tmcd... I will look for instructions for it and try it on a couple of test machines before trying it with a live server and one of them

[apaton]

I forget the term, I think it's called a 'differencing file' where by each VM sees a read-only copy of the master VM and have their own writable file where they store their own changes (or differences) to the master VM.

I believe this feature is supported by ESX and it can be done with VMDK's. Can't remember what is called though. But yes it is actually possible to do what you want.

Each VM sees the VMDK as a unique drive to them rather than a single cluster chared volume. No data corruption occurs because the difference are written to the differencing file and not the share VMDK.

Are you referring to linked clones?
In Vmware ESX linked clones option was provided with View composer only. (VDI)

Andy

[tmcd35]

This sums up what I was thinking off...

Running multiple virtual machines on one VMDK - NTPRO.NL

Put the original VMDK in snapshot mode and add it as a non-persistant disk to the other VM's. Each VM then has it's own snapshot file detailing the differences between it and the original.

[apaton]

Put the original VMDK in snapshot mode and add it as a non-persistant disk to the other VM's. Each VM then has it's own snapshot file detailing the differences between it and the original.

TMCD35, this sound like a fore-runner to linked clones , nice hack!


But getting back to DAckroyd question

Does anyone know if you can use the same VMDK on 2 VM's?
................
I was wondering if while I was setting up the new servers whether I could share the VMDK so data on the 2 servers was identical. ....

I understand this to mean the same VMDK disk file, so two servers have the same data, ie VM-A writes data, VM-B can see it instantly.

Have I totally misunderstood the question ?

DAckroyd could you clarify please.

[DAckroyd]

I understand this to mean the same VMDK disk file, so two servers have the same data, ie VM-A writes data, VM-B can see it instantly.

Have I totally misunderstood the question ?

DAckroyd could you clarify please.

you are spot on... it's the data drives not the OS drive

i have 2 VM's atm, created a small data drive and have tried connecting vm2 to vm1's data drive - wouldnt do it turned on so turned off the vm with the data drive and tried connecting again. i have just rebooted the vm trying to get the data drive and it's come up. just had to activate drive and assign letter.

i will now attempt to boot the other vm at the same time


hope that makes sense

//update\\

cannot power on: Unable to access a file sinse it is locked

[apaton]

you are spot on... it's the data drives not the OS drive
............
cannot power on: Unable to access a file sinse it is locked

Yes, absolutely will not work.
Only way to map the same virtual disk (not snapshot) to two VMs simultaneously in VMWARE is using a RDM.
Then you have issues around locking, corruption etc.. with NTFS, unless is a correctly configured cluster configuration.

Andy

[DAckroyd]

I don't have much worry about disk space - is there a way that I can set VMware to copy the VMDK and keep it upto date/syncronised??

[apaton]

Option 1,
Create a new virtual disk and use tools like RSYNC to keep the upto date, but that's more Windows Forum question.

Option 2,
From the VMWARE side,

1. Shutdown source VM
2. Copy VMDK file to new destination
3. Assign VMDK file to new VM.

Andy