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Re: FSFS packing functionally complete

From: Andreas Schweigstill <andreas_at_schweigstill.de>
Date: Fri, 28 Nov 2008 09:30:57 +0100


Hyrum K. Wright schrieb:
> Because we store lots of little files with FSFS, we take a space hit. Using an
> example sector size of 4kB, and assuming the size of the files modulo the sector
> size is uniformly distributed, we can probabilistically state a 2kB waste of
> space *per revision*. For our repository, that would mean 34.5 k * 2 kB = ~70
> MB of wasted space[1], in a ~450 MB repository, by no means trivial. By
> smashing the little files together, we reduce this internal fragmentation in the
> file system, and increase space efficiency. Additionally, larger files are
> easier for the file system and operating system to handle in many cases, and may
> help with our own internal caching.

But when putting multiple revisions into one big file there occurs a new
problem. Skript like svn-fast-backup.py depend on the current
implementation of just one revision per file. For doing forensic
investigations on currupted repositories and backup/restore purposes
it is also much better to have files in the repository which will never
change once they have be created in order to store a certain revision.
So finally I am not sure that there will be some space saving at all if
you also take into account that for backup purposes the "big revision
file" will exist several times on the system. Instead hard linking to
existing files which should never change is quite "cheap".

With best regards
Andreas Schweigstill

Dipl.-Phys. Andreas Schweigstill
Schweigstill IT | Embedded Systems
Schauenburgerstraße 116, D-24118 Kiel, Germany
Phone: (+49) 431 5606-435, Fax: (+49) 431 5606-436
Mobile: (+49) 171 6921973, Web: http://www.schweigstill.de/
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Received on 2008-11-28 09:29:22 CET

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