Physical Mode RDMs and SRM

[ngms27]

I have Physical Mode RDMs on a FalconStor system. The FalconStor agents create Application Consistent snapshots of the Applications.

Are these RDMs supported by SRM?

[MarekZdrojewski]

Hi,

Generally speaking, yes. Site Recovery Manager provides full support for virtual machines using RDMs but depending on version of SRM you want to use, please read the release notes for know issues.

hope this helps.

Cheers!

[mal_michael]

Hi,

RDMs in physical and virtual compatibility mode are fully supported for years.

Michael.

[TomHowarth]

Yes phyiscal mode RDM's are fully supported from version 4.0 onwards, just remember that they too have to be replicated between both arrays.

[kgottleib]

Sorry folks - I'm having a hard time believing what I'm reading in this post -

I realize VMware says its supported - but I still need more.  Having worked with VMware in DR events, and have worked extensively with pRDMs, I have serious doubts on this and would prefer if someone who has actually performed a full blown test, or have the technical deep dive please chime in on this.

I realize the VM guest OS at the DR site can and will see the exact same data on the its data drive \ pRDM \ LUN after it is mounted.  but ESXi on the DR site sees the replicated LUNs as snapshots and need to resignature them (LVM resignature = 1), so how does SRM manage to get this snapshot LUN mounted to the replicated VM so it can power on normally and see its data on this drive?

Sorry for being a doubting Thomas.. but I would prefer a validation check on this from someone?  this is important for me to get to the bottom of quickly otherwise I would build this out in my lab and test it to be certain..

[TimOudin]

Presuming replication, supported SRA, etc. then SRM handles RDM brilliantly.  I've had RDM in environments personally as well as having multiple clients.  The point about resignature and snapshot detection doesn't apply here as that is based entirely on the disk ID of a VMFS file system.

TIm Oudin

[kgottleib]

TI'm - your reply kind emphasizes my concern - a pRDM does not contain a VMFS file system - it is mapped directly to vm and then formatted by the guestOS as ntfs or ext3 etc...  Is the disk ID independent of VMFS?

[TimOudin · Accepted solution]

The reply should do the exact opposite for your concerns, but I left out some detail so I'll try to clear that up.

The signature in question is an element of the logical volume manager, is comprised of the LUN ID(s) as seen by the ESXi host and the disk serial number(s) of the LUN(s) of the datastore.  This value is written as metadata in the VMFS volume header.  In the case of an RDM, there is no VMFS filesystem, therefore there is no signature to worry about.

http://www.vmware.com/files/pdf/vmfs_resig.pdf

Cheers

Tim Oudin

[kgottleib]

Got it!  thanks for the thorough explanation, well done.