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

quoted text
> On Fri, 02 Nov 2007 23:08:23 -0400
> Valdis.Kletnieks@vt.edu 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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