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SubjectRe: [OFFTOPIC] Re: disk head scheduling
Date
In article <14070.58301.339007.437665@dukat.scot.redhat.com>,
Stephen C. Tweedie <sct@redhat.com> wrote:
>Hi,
>
>On Sun, 21 Mar 1999 11:49:31 -0800, jg@pa.dec.com (Jim Gettys) said:
>
>indexed by block numbers). If the filesystem can also deallocate such
>space, then we have an abstraction behind which filesystem shrinking

As a side-effect this would help make devices built on FLASH memory a little
easier to deal with. FLASH has the interesting principle of being able to
be written from 1 to 0 at any time, But writing a 0 to a 1 requires erasing
a (relatively) large block. The end result is that rewriting a single block
can involve copying about 100k of data from one area to another.

If the filesystem can tell the device layer that a block is no longer being
used then the device layer can stop moving it around when erasing. This not
only speeds that operation but opens up more empty space to copy new data
to. [The device layer doesn't erase to rewrite blocks, it marks it as unused
and writes it to somewhere that is currently not being used. It only erases
when it runs out of empty blocks and needs to recover some.]

--
Stuart Lynne <sl@fireplug.net> 604-461-7532 <http://edge.fireplug.net>
PGP Fingerprint: 28 E2 A0 15 99 62 9A 00 88 EC A3 EE 2D 1C 15 68

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