From: rajat@watson.ibm.com (Rajat Datta) Subject: Re: New feature for the filesystems. What do you think ? Date: Mon, 19 Apr 1993 18:51:23 GMT
In article <pdhC5pw6L.5t8@netcom.com> pdh@netcom.com (P D H) writes:
>
>This assumes all blocks can be compressed to 1/2 size. I had hoped
>such assumptions were readable only in the Nation Enquirer, but I guess
>I am wrong.
>
If it doesn't compress then you write it out to the full size block
(the non-compressed stuff). There are at least 2 blocksizes.
>It's one thing compress a block of data. It's yet another thing to take
>advantage of that compression by writing something else in the rest of
>the block. And since you don't always get 512 bytes from 1024 bytes of
>data, the remaining size available cannot be guaranteed to be 512 bytes.
>
>Assume the hard disk has 1048576 blocks of 1024 bytes each. How many
>blocks do you make the file system for?
You don't get perfect disk savings of course. If you maintain four
possible block sizes, for example, 25%, 50%, 75% and 100%, then you
pick the one that the compressed size is closest too and smaller. You
ignore the rest of the block.
-- rajat (rajat@watson.ibm.com)