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You're backing up the back up ... on the drive that you were backing up?
Authored by: maikel on Aug 10, '08 11:02:38AM

I found out that the option of using sparse bundles can go wrong too easily. Essentially, the sparsebundle consists of thousands of small files that together are mounted as a file system. After trying rigorously to make my nslu2 work as NAS that, through mounting the sparsebundle files were trusted, I found that solution not reliable; every two weeks I had to restart as the sparsebundle to back up my iMac would go south, requiring me to start ... again and again.

This hint could help the restart process, picking up from a particular incremental backup. It is obviously not a good idea to copy a backup back to the backed-up drive as when that drive is lost, so are the files. In case your sparsebundle happens to be crippled at the same time, you're in shit.

As for the one big file comment; the backup itsself is written to the Volume that you mount from the sparsebundle. The backup of all the files is written to this volume, which in turn is persisted as thousands of files that represent that Volume. In theory, this would reduce the chances of loosing data due to unreliable network access.

In theory, yes. I had to move away from the NAS approach; sadly it's not reliable enough. I found that checking the volume with even ONE missing file-segment would cripple the entire bundle.


Each back up <i>looks</i> like it is a complete copy of all the files. Instead this is so called hard-links at work. Very smart way of double using unchanged files; the entire directory structure is indeed replicated in each backup, instead of being incremental. Yet, all of the unchanged files are only on the bundle once, with a use-counter. Once the last reference to that file is removed, so will the file be. Very smart IF your files are small, rather than big binaries.

Good thing iPhoto library looks like a single file, but actually is a package comprised of the underlying photos and metadata. Also Mail uses many many small files. So where M$ Outlook would touch the OST or PST file of 500mb and change it, Apple actually made its persistance very lean to back up incrementally.

I ended up using a plain hard disk in the neighborhood. I have no idea how the time capsule circumvents the above issue.



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