For years, I’ve been afraid of RDMs. But this week I faced my fears, and I’m sure glad I did!
Are you interested in RDMs? Well, RDMs, or Raw Device Mappings, are a nifty storage virtualization technique that just might allow you to take hard drives from an aging system, move them to an ESXi system, then boot them in a virtual machine. Yes, you read that correctly, no cloning or long conversion required. In other words, the hard drive itself is essentially passed through to the virtual machine.
Unlike methods of VMDirectPath / VT-d / passthrough of SATA or USB 3.0 ports, this method allows you to use your motherboard’s SATA ports. Here’s the kicker. Once you’re virtual, you are then also able to migrate all the data to a more traditional ESXi 5.0 datastore, such as a fast RAID array, so your old machine now runs much faster, and you can take those original hard drives back out. You can even try to boot them on the original physical machine again, if you wish.
I need to be clear: if you have a system that you could use VMware Converter Standalone 5.0 on, to easily copy the entire PC and all its data into a virtual machine, that’s the easy and preferred and free way.
But what if such a simple tool isn’t an option, for reasons such as:
Scenario 1: Hardware Failure
The RDM technique could also be handy if an old system’s power supply dies one day, and you don’t wish to put more money into that old system, and you’re keen on just getting going again. Let’s also assume all that data is backed up as well (true for all my posts). Then this technique I’ll be documenting, may just be able to get you going again.
Scenario 2: Special Filesystems
What if you can’t mess with the NTFS file system on your old box, such as if you’ve implemented software RAID (Dynamic Volumes in Windows) across multiple disks, or perhaps have a D drive that is really a set of physical disk joined with Microsoft Drive Extender (Windows Home Server). These circumstances might not allow traditional conversion and/or cloning tools to move the data to a VM (VMware Converter, Acronis, Ghost, EaseUS Disk Copy, etc). My own experience with sector-by-sector cloning has been met with mixed results, and 5 day cloning times for 5TB of data, not good. Getting going in minutes sounds better.
While RDMs for SATA drives are not best practices, and you’ll have some crud to clean out of Device Manager in the VM, doesn’t it seem worth a try?
Now are you interested in RDMs?
David Warburton has expertly documented many of the techniques here, and my future posts will also cover prep for boot (BIOS settings and VM settings to avoid BSODs), what to do with RDMs after you get them booted, and how to remove them cleanly as well.
I’ve also recorded some detailed video walk-thrus of the process as well.
Despite all that help, this will never be your grandmother’s P2V. This risky project is not for the feint of heart. Enough disclaimers?
Please comment below, to let us know your interest in this admittedly intermediate-to-advanced level project!
*I should warn you, using RDMs to essentially trick ESXi 5.0 into seeing a SATA drives as a SAN is entirely unsupported by VMware, and it’s your responsibility to backup all your data before such “lab tests”
Update Dec 23 2011: Great news, it works, I mean, conversion after booting works! The 2 1/3 day VMware Converter task, which copied all 5TB of the RDM (actual data on SATA drives) to traditional VMware drives, which are VMDK files living on a VMFS filesystem. This is great, I can finally re-use the 1.5TB drives from the source system, knowing the entire physical system now lives on in the virtual world!
I have a lot of new blog posts to work on next week to better explain all this, and a longer series of videos.
Future posts and videos will cover my numerous clone-based and migration based failed attempts, then finally my successful VMware vCenter Converter Standalone 5 conversion.
For now, this video is ready, that shows exactly how I configured ESXi 5.0 RDMs to allow me to boot a 4 SATA drive-set (5TB total data) that were pulled from a physical machine, and quickly booted in a virtual machine, no data copy or conversion required! This was an unrehearsed, live view of the work I did this week, where you’ll hear me think aloud.