[OpenAFS] openafs on Fedora 12?
Chas Williams (CONTRACTOR)
Thu, 10 Dec 2009 08:16:45 -0500
In message <4B20B344.email@example.com>,Rainer Toebbicke writes:
>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;
ah. i did indeed forget this point. this is particular annoying with
regard to memcache (it causes a realloc of the chunk if the chunk is
undersized). for now, we could ensure that chunk sizes are 'sufficiently'
>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;
i dont ever wish to free parts of a file. i just wanted to create the
file quickly to avoid making the user wait while a 1GB is written.
oversubscribing /usr/vice/cache is somewhat like asking the doctor why
it hurts when you hit yourself with a hammer.
>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 am not convinced that the well placed truncate calls have any meaning.
the filesystems in question tend to just do what they want.