Re: WANTED: kernel projects for CS students

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On Fri, 2 Nov 2007, Rik van Riel wrote:

On Fri, 02 Nov 2007 23:08:23 -0400
[email protected] wrote:

IBM's AIX supported file system compression on the JFS filesystem
years ago. I was able to get up to 30% throughput increases by
converting the /usr filesystem to compressed - because even a 33mhz
Power chipset could read in 5 512-byte blocks and decompress it to
the original 4K faster than the disk could read in 8 512-byte
blocks.

Given that today there's an even *bigger* disparity in CPU speed
versus disk speed, I'd be surprised if it doesn't help today too.

The problem is that disk seek times have not gotten much
faster over the years, while disk throughput rates have
skyrocketed.

Transferring a little less data is not going to help you
when 80% of your disk time is spent seeking, not reading
or writing.

however, if you can manage to avoid seeks by packing more data onto each track (or each stripe of a raid array) you could probably see a significant win

that's something for aspiring (and experianced) filesystem designers to struggle with for a while (especially trying to figure out what the size of a track or stripe is for the optimal layout)

David Lang
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