Pros and Cons of VMFS using multi-writer flag

[arushanm]

Hi All,

What are the pros and cons of VMware VMFS multi-writer flag ?

Thanks

Arumuga Raj

[npadmani]

Please look into official KB article published by VMware

http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=103416...

This will give you clear understading of usecases, and that will help you to understand pros and cons too.

[arushanm]

Is it possible to create a shared virtual disk (.vmdk) between two vms ? using VMFS multi-writer flag.

If it is possible means the VMFS multi-writer flag is disable.

And also I came to know that the VMFS multi-writer flag is always in disabling mode.

My question is if I enabling the VMFS multi-writer flag. What are the pros and cons ?

1. Whether the Data or VM could corrupt .?

2. Can we access the virtual disk without any downtime ?

Please advice the same for in clustering perspective.

Thanks

Arumuga Raj

[npadmani]

yes muti-writer by default is disabled

but if you wish to share a VMDK between two VMs, yes it's possible (how to do that, the KB link I shared earlier has got it in step by step)

From clustering perspective

we should enable muti-writer only when we know a cluster aware application which is going to be installed across two or more VMs itself takes care of concurrent read/write in a way that we don't have to worry about data loss.

but let's say you have enabled muti -writer for a vmdk and shared it across two VMs which doesn't have such mechanism (like cluster aware application service), we are definitely at a risk of data loss.

[continuum]

There are no Pros at all.
You simply always leave that flag in the disabled default settings - unless you really MUST enable it because you want to use one of the handful of rare constellations that would not work otherwise.

If you enable it and do not use guests that can handle cluster-access you will very quickly learn never to try this again.
5 minutes can be more than enough ...

IMHO the term sabotage is quite appropriate when you use this flag with VMs that are not configured for Fault Tolerance or for guests that are not cluster-ready.