[OpenAFS] openafs on Fedora 12?
Thu, 10 Dec 2009 09:37:24 +0100
Chas Williams (CONTRACTOR) wrote:
> i still wonder if the cache manager shouldnt open a single file (sparse
> mode) and just seek/read/write. this would solve a couple of potential
> problems with other filesystems as well.
There are some issues with the canonical approach of just using one file and
seek to chunkno*chunksize:
1. directories are read in total, regardless of chunk boundaries;
2. it is, to my knowledge and on a POSIX level, not possible to "free" parts
of a file. Hence, if the number of chunks in the cache exceeds the size of
/usr/vice/cache you run out of space;
3. unless done carefully, if you re-write parts of a file the system may end
up reading it in first (partial blocks).
With individual cache files and well-placed truncate() calls these issues go
I guess none of those are unsolvable, having just a single file (or set of
files on different discs) could make life easier and speed up things by
eliminating double buffering (afs's VM cache + cache chunks's VM cache).
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