mcachefs is a simple caching filesystem for Linux using FUSE. It works by copying the file that you asked for when the file is opened, and then using that copy for all subsequent requests for the file. This is really a fairly naive approach to caching, and will be improved in the future. It's good enough for now though.
mcachefs needs two filesystems to operate. The target filesystem is the slow filesystem you want to cache accesses to, and the backing filesystem is where mcachefs can stash stuff which it has copied. The backing filesystem should therefore be on local disc, or the whole point of the exercise is gone.
It is also assumed that the target filesystem is read only for now.
Installing:
You'll need FUSE, so your best bet is to go up a directory level, and then type:
./configure make make install
(That last step needs to be done as root of course).
Using:
mcachefs looks for a config file to determine where the target and backing filesystems are located, as well as a debugging verbosity level. mcachefs looks in the following locations for it's config file (in this order):
- /etc/mcachefs
- ~/.mcachefs
- `pwd`/mcachefs.cfg
/cache/backing /backing /cache/target / /cache/verbose 99
Note that the two columns must be separated by tabs for the config file to parse properly. This config section above says that we have a cached filesystem to mount at /cache. The backing store is /backing, the target store is /, and we want to be _very_ verbose. Lower numbers are less verbose. Please note that being very verbose might help with debugging mcachefs, but _will_ slow down the filesystem.
You can now mount the cached filesystem but doing a:
mcachefs /cache
This program wont terminate... If you kill it, the filesystem will unmount. Don't do that. Use umount instead. I have making mcachefs daemonise on the todo list, so don't bother reporting it as a bug please.
Known bugs:
The only known bug at the moment is that if the program which is opening a large file terminateds before the cached copy has been generated, then a bus error occurs in mcachefs. I'm looking into that now.
So, I came up with this great patch:
Email me at mikal@stillhq.com
New code?
You can find the latest version of the code at http://www.stillhq.com/extracted/fuse, and http://www.stillhq.com/extracted/fuse.tgz
posted at: 21:03 | path: /site | permanent link to this entry