Compete PC Backup and wbadmin

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Tim - 24 Jan 2007 14:41 GMT

I'm going to be using wbadmin to do backups so they can be done on a
schedule. With Complete PC Backup, if there is already a backup file
present, you are presented with following dialog:

"The backup could take up to 157 GB of disk space. Because a previous
backup already exists, all of this space might not be required, and only the
differences will be saved. If there is not enough space on the disk, one or
more of the older backups will be discarded starting with the oldest."

Does wbadmin do the same thing? Are subsequent backups differential only?
I see no command line switch to set this one way or the other. Also, will
wbadmin automatically delete older backups to free up disk space? Thanks
for any help.

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Jill Zoeller [MSFT] - 24 Jan 2007 16:37 GMT

Wbadmin is the command-line version of Complete PC Backup and they both work
the same way. So yes, when backing up to disk, subsequent backups are
differential and stored as shadow copies. Older shadow copies are purged
when the shadow copy storage area becomes full.

You might find this blog post useful:
http://blogs.technet.com/filecab/archive/2006/11/16/identifying-how-much-disk-sp
ace-is-used-for-restore-points-in-windows-vista.aspx

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> I'm going to be using wbadmin to do backups so they can be done on a
> schedule. With Complete PC Backup, if there is already a backup file
[quoted text clipped - 10 lines]
> wbadmin automatically delete older backups to free up disk space? Thanks
> for any help.

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Tim - 25 Jan 2007 00:15 GMT

Thanks for the link. While we're on this subject, I have some other
questions since I know little about shadow copies. My understanding is that
the first backup file is a .vhd file, and subsequent differential backups
are shadow copies. If, for example, the only change in the volume is the
deletion of one file, what gets stored in the shadow copy? Is it just an
indicator that the file has been deleted? Does this take up space? Say,
for example that the only change is one file being added. Will the shadow
copy only contain this one file? If that file is later deleted, will that
shadow copy also be deleted? If I perform a backup every day, is the shadow
copy composed of the difference between today's configuration and the
original .vhd file, or today's configuration and the original .vhd file plus
all subsequent shadow copies? I guess my concern here is that the totality
of the backups will eventually be much larger than the current drive being
backed up. Is this the way it works? Thanks.

> Wbadmin is the command-line version of Complete PC Backup and they both
> work the same way. So yes, when backing up to disk, subsequent backups are
[quoted text clipped - 18 lines]
>> Also, will wbadmin automatically delete older backups to free up disk
>> space? Thanks for any help.

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Jill Zoeller [MSFT] - 26 Jan 2007 20:53 GMT

Hi Tim,
To answer your questions:

> Thanks for the link. While we're on this subject, I have some other
> questions since I know little about shadow copies. My understanding is
> that the first backup file is a .vhd file, and subsequent differential
> backups are shadow copies. If, for example, the only change in the volume
> is the deletion of one file, what gets stored in the shadow copy?

Nothing changes until the blocks previously occupied by the file are
overwritten.
In general, every block level change on the volume will consume space on the
shadow copy storage area. But file deletions by them selved don't amount to
much.

Is it just an

> indicator that the file has been deleted? Does this take up space? Say,
> for example that the only change is one file being added. Will the shadow
[quoted text clipped - 5 lines]
> the totality of the backups will eventually be much larger than the
> current drive being backed up. Is this the way it works?

The last statement could be true depending on how many shadow copies you
keep and your usage patterns. If you backed up and then overwrote your
entire volume and backed up again, you would consume twice the space.

We have a slide presentation somewhere that illustrates this. If I find it,
I can email it to you. I don't think it's NDA.

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> Thanks for the link. While we're on this subject, I have some other
> questions since I know little about shadow copies. My understanding is
[quoted text clipped - 34 lines]
>>> Also, will wbadmin automatically delete older backups to free up disk
>>> space? Thanks for any help.

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