Ultimate backup doesn't compress image?

[DevilsPGD]

In message <[email protected]> "Jill Zoeller [MSFT]"

"That explanation partially makes sense (although only to a point -- It's
possible to engineer around the problem"

We get a lot of questions like "Why didn't you add X," and often the reason
boils down to time.The guys on the dev team never look happy when they
explain this to me. They made a lot of tradeoffs for Vista and are looking
at those for future releases.

Understood -- And I spend a substantial percentage of my week explaining
the same to my distribution channels for my employer's software.

Thanks for the info!

 

[Rock]

Thanks Jill.

"Copy-on-write" is Volume ShadowCopy (VSS) terminology. Complete PC Backup
uses shadow copies to store the incremental changes to .vhd file. These
updates are stored in a hidden area on your hard disk. This area is
configurable and can only hold so many shadow copies. Once the area fills,
oldest shadow copies are purged. The more changes on the volume, the more
quickly those older shadow copies will be purged. From what the developer
explained, the act of compressing a .vhd causes it to change more from
version to version. We want to avoid having those older shadow copies
purged, so we don't compress the .vhd on hard disks.

You can find explanations of "copy-on-write" in the Technical Reference at
http://technet2.microsoft.com/Windo...b7d8-42c3-b6c9-59c145b7765f1033.mspx?mfr=true.
Some google searching also turns up good hits. I'll ask the VSS team if
they can give a step-by-step description of what happens.

Here's a link to our blog for more info on shadow copies:
http://blogs.technet.com/filecab/ar...used-for-restore-points-in-windows-vista.aspx.

I can't speak for Acronis--do they use VSS?

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On Wed, 31 Jan 2007 10:03:29 -0800, "Jill Zoeller [MSFT]"

Here's the reason: On the incremental backup, any compression would lead
to
huge differences between the current vhd and the one on the snapshot and
we
will be deleting old snapshots at much higher rate. So the backup
algorithm
is highly optimized to cause as little as possible copy-on-write to be
able
to keep more backups on the target disk.

Wow does that sound like a bunch of mobo jumbo.
Why doesn't Arconis have this problem? BTW what is COPY-ON-WRITE and
couldn't you keep even more backups if they were compressed?

All very good questions.