Re: [BackupPC-users] Backup of VM images

Boniforti Flavio <flavio AT piramide DOT ch> wrote on 06/07/2011 12:22:18 PM: > Could you please depict a bit more in depth this part? > AFAIU, if I do too many incrementals I'd have to take in account growing > backup times from differential to differential. > On the other hand, if I'd do only full backups, I'd have way longer backup > times, for *each* single backup shot.
Not in this case.

In a "normal" (data in zillions of files) environment, an incremental backup can skip reading 99% of the files because they will not have changed. In a "VM" (data in a few very large files) environment, every one of the files will have changed every day. Therefore, both incrementals and fulls will read *exactly* the same amount of data: all of it.

The only difference between fulls and incrementals, then, is how much data is *transferred*. Incrementals will grow during the week: if you change an average of 1GB per day, then the incremental will transfer 1GB on the first day, 2GB on the second, 3GB on the third, etc. until it does the next full, when it will then reset and start again.

That, by the way, is *exactly* the same thing that will happen in a "normal" enviornment, too. Most of us simply do not care, even in low-bandwidth environments, because our deltas are still small enough that it really doesn't matter. For example, my incrementals on a remote office vary from 30 minutes to 300 minutes. 5 hours in the middle of the night is not at all an issue for me.

Anyway, I stand by my (and most everyone else's) point: BackupPC will do this job fine. HOWEVER, the usage pattern of this project does *not* fit the strengths of BackupPC: you will get almost no advantage from using BackupPC than most any other tool. In fact, most of the features of BackupPC (pooling and long-term aging) are completely useless for this application.

By the way, I have seen very little acknowledgement on your part of what is by *far* the hardest part of snapshot-level backups: the snapshots. How are you quiescing the targets? How are you getting exclusive access to the datafiles? Will it result in downtime for your VM's and is that acceptable? If not, how are you getting around this?

Backup at the VM level looks *nothing* like backup at the filesystem level, and most people have almost no understanding of this. You are *far* from alone in this, which is why there are a bunch of companies that make snapshot-level tools for backup for VM's. They are *far* superior to trying to bend your thumb back to your wrist and make BackupPC do the job.

Timothy J. Massey


Out of the Box Solutions, Inc. Creative IT Solutions Made Simple! http://www.OutOfTheBoxSolutions.com tmassey AT obscorp DOT com		22108 Harper Ave. St. Clair Shores, MI 48080 Office: (800)750-4OBS (4627) Cell: (586)945-8796

------------------------------------------------------------------------------
EditLive Enterprise is the world's most technically advanced content
authoring tool. Experience the power of Track Changes, Inline Image
Editing and ensure content is compliant with Accessibility Checking.
http://p.sf.net/sfu/ephox-dev2dev

_______________________________________________
BackupPC-users mailing list
BackupPC-users AT lists.sourceforge DOT net
List:    https://lists.sourceforge.net/lists/listinfo/backuppc-users
Wiki:    http://backuppc.wiki.sourceforge.net
Project: http://backuppc.sourceforge.net/