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Fri, 06 Jun 2008

POHMELFS development status.

POHMELFS got ability to add/remove servers in run-time (although not via network command, since I do not know, how to test it yet), but via netlink interface. The same message can be passed via network though, so it will be simple to extend.
Also, POHMELFS got readahead support via ->readpages() callback. I removed AIO reading from POHMELFS in favour of readahead and got excellent result in sequential reading: 3-3.5 times faster than NFS and essentially reaching disk IO bandwidth (a bit less though), but random reading dropped to miserable numbers.
Also rewritten reading method should provide better balanced between multiple servers capabilities for the system, but it will not show any benefit in single-threaded iozone benchmark, since it reads data via single call to read(), which gets sequential data access, which in turn is faster than network bandwidth. So multithreaded load should greatly benefit from read balancing, but I did not yet test that.

I ran sequential read/reread, write/rewrite and random read/write tests for XFS, Ext4, NFS (over XFS) and POHMELFS (over XFS) with 1Gb of RAM and 8Gb of test files (to eliminate VFS caching influence) with 8Kb to 1Mb record size.
Results exist in text files in standard iozone output format, but since I'm learning LISP I decided to write a graph generator (via gnuplot) using my very basic knowledge of this language, so nice graph results can take a while...

Also, tomorrow morning I will flight away to my friends marriage and will only return monday 9. I will not have internet access there, only lots of fun.

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