A question about rsync

[Ben Scott]

On 7/23/07, Flaherty, Patrick <pflaherty at wsi.com> wrote:
> The other issue was locked files over smb. Outlook data
> file (.pst?) wouldn't backup correctly because they were opened in some
> odd mode.

  In general, files can only be reliably backed up if they are
quiescent.  Otherwise, you're likely to get the file in an
inconsistent state when the backup software grabs it.  This is true
even for filesystem-level snapshots and "open file backup" products,
let alone regular file I/O (which rsync uses, and it looks like
BackupPC does also).  While a snapshot mechanism may be able to ensure
the whole file is consistent as stored at an instant in time, if that
instant happens to be when the application is in the middle of
updating it, you're still going to end up with a scrambled file.

  Essentially, upon restore, the application will see things as if you
had killed the power to the system at the instant the backup ran.
Depending on the nature of the file and the intelligence of the
application, recovery at that point may be easy, hard, or impossible.
PST files tend to fall more towards the "hard" end of the spectrum.

-- Ben