Scott Waterhouse finalized his thoughts on the whole VMware backup idea on his blog today. One of the things he said that surprised me was that, while you can’t get application-consistent backups in VMware without the use of a host-level agent, you can get crash-consistent backups. My response is simply this: I’m sorry, that is not even close to the MINIMUM requirement of what you need.
I’m frankly amazed that Scott would post this, as he is a backup person and knows better. He knows that crash-consistent backups are as trustworthy as a 1978 Pinto’s gas tank. So who cares if you can make them?
Besides being untrustworthy, they miss one of my critical points here: If you’re not doing a full VSS implementation (which they aren’t — even on Windows 2003) then the applications won’t know they’ve been backed up. Even if you get a <cough> crash-consistent backup, you’ll still need an agent to dump to tell the application that it’s been backed up so it can dump it’s transaction logs. Otherwise they’ll fill up and the app will crash.
But back to crash-consistent backups… What does that mean? it means you are backing up an image of the VM that is EXACTLY equivalent to doing the following:
1. Yank the power cord from your favorite server (no shut down, no quiesce, just yank the power cord out of the UPS)
2. Plug it’s now confused filesystem into another server
3. Don’t fsck it or anything
4. Just back up the bits
If you have to restore it, the server and its apps will need to go through a crash recovery process, and it will work most of the time. But HEY! The fact that servers don’t always come up after a crash is one of the reasons we take backups! So why the (*%% would you trust that method as the backup? I wouldn’t, never have, and never will.
So to summarize. Without an agent in each VMware VM:
1. You’ll get a <gag> crash consistent backup
2. The apps won’t know they’ve been backed up, their logs will fill up and the app will crash
Unless you get an agent. Which was the whole point.
----- Signature and Disclaimer -----
Written by W. Curtis Preston (@wcpreston). For those of you unfamiliar with my work, I've specialized in backup & recovery since 1993. I've written the O'Reilly books on backup and have worked with a number of native and commercial tools. I am now Chief Technical Architect at Druva, the leading provider of cloud-based data protection and data management tools for endpoints, infrastructure, and cloud applications. These posts reflect my own opinion and are not necessarily the opinion of my employer.