Dropping mode optimization from Metafile?

Richard Edward Horner rich at richhorner.com
Wed Aug 29 01:51:58 UTC 2007

Well, permissions are important for backing up if you're running a
hosting company or some such.

What distros are you using? It's Debian Etch, Gentoo (well, Sabayon
4.3e) and SLES10 over here.

Thanks, Rich(ard)

On 8/29/07, robb <robb at canfield.com> wrote:
> I currently hacked in the "standard" permissions for files and dirs
> where standard is what my 3 distributions use! Other solutions are
> possible but I can't help but wonder if its 90% work for for 1% gain, so
> I am not pursuing them right now.
> Richard Edward Horner wrote:
> > I'd say bring this up again when Brad gets back from camping or
> > whatever because he probably has reasons for this architecture but I
> > do agree that the issues you point out are unfortunate.
> >
> > Thanks, Rich(ard)
> >
> > On 8/28/07, robb <robb at canfield.com> wrote:
> >> During a test of a medium scale backup (simulating RAM and directory
> >> overhead for 77,000 files averaging 1 MB) I am finding some higher than
> >> desired RAM usage.
> >>
> >> Brackup buffers all of the file stats in RAM (something that is a bit
> >> tricky to change). This is a constant for the run, but Brackup also
> >> buffers all chunk data until the backup is done and the metafile
> >> written. This chunk data can add up to a considerable amount of usage.
> >> The main reason for buffering chunk data seems to be to optimize the
> >> size of the file by remembering the most common file and directory
> >> modes. If the file/dir is the default mode then the mode line need not
> >> be added.
> >>
> >> While optimizing the size of a file is always nice, the downsides for
> >> large backups may overshadow this:
> >>
> >> - A failure during backup leaves then brackup metafile out of date (or
> >> non-existent). Even if MANY files are properly saved,, the index to them
> >> is not available.
> >>
> >> - RAM is consumed and CPU resources used for saving this data in RAM.
> >> This becomes an issue on virtualized systems with low RAM thresholds OR
> >> for any system with LARGE data sets. Brackup currently stores the entire
> >> file list in RAM, but during backup the chunk references are added to
> >> this and it is those chunk references that start to add up for large
> >> files or large backup sets and small a small chunk size makes it even worse.
> >>
> >> - The optimization is relatively small (actually very small) size wise
> >> given the other data in the file.
> >>
> >> I vote to drop the optimization file size and favor RAM (and execution
> >> speed) by streaming the metafile as each file is finished. Any thoughts?
> >>
> >>
> >
> >

Richard Edward Horner
Engineer / Composer / Electric Guitar Virtuoso
rich at richhorner.com
http://richhorner.com - updated June 28th

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