Boniforti Flavio <[email protected]> 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
[email protected]
22108 Harper Ave.
St. Clair Shores, MI 48080
Office: (800)750-4OBS (4627)
Cell: (586)945-8796
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