Messages in this thread | | | Date | Wed, 15 Oct 2003 11:37:19 -0600 | From | Andreas Dilger <> | Subject | Re: Transparent compression in the FS |
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On Oct 15, 2003 13:19 -0400, Richard B. Johnson wrote: > On Wed, 15 Oct 2003, Nikita Danilov wrote: > > It could not if block-level compression is used. Which is the only > > solution, given random-access to file bodies. > > Then the degenerative case is no compression at all. There is no > advantage to writing a block that is 1/N full of compressed data. > You end up having to write the whole block anyway.
In the ext2 compression code, they compress maybe 8 source blocks into (hopefully) some smaller number of compressed blocks. Yes, there is still a minimum block size, but you can save some reasonable fraction of the total space (e.g. 8 blocks down to 4.5 blocks still gives you 5/8 = 37% compression, although not 50%). You get more efficient compression the more source blocks you use, although your "damage area" grows in case of error.
Cheers, Andreas -- Andreas Dilger http://sourceforge.net/projects/ext2resize/ http://www-mddsp.enel.ucalgary.ca/People/adilger/
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