Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!mailrus!ames!necntc!dandelion!ulowell!page
From: page@swan.ulowell.edu (Bob Page)
Newsgroups: comp.sys.amiga
Subject: Re: Fast File System questions
Summary: Answers
Message-ID: <8372@swan.ulowell.edu>
Date: 1 Aug 88 04:08:23 GMT
References: <260@geocub.UUCP>
Reply-To: page@swan.ulowell.edu (Bob Page)
Organization: University of Lowell, Computer Science Dept.
Lines: 48

anthes@geocub.UUCP (Franklin Anthes) wrote:
> - is FFS a totally new FS, or just changes made to the old FS?

Changes made to the old FS.  But it's totally new (written from scratch,
in assembler, and not in ROM).

> - What changes have been made?

It no longer stores the 24-bytes of 'header' information in data blocks,
so can now do multi-block DMA transfers to the user's buffer (if the
controller and application support it) since it's just 512 bytes of
real data per block.

It also hashes the files differently for much faster directory searching.

It supports a LOCK/UNLOCK dos packet to write (and read?) lock your disk.

It does some other things differently (like pre-allocating bitmap blocks)
but I don't think you want that kind of detail.

> - Why does FFS for diskettes have to wait until 1.4?

Because trackdisk.device is in ROM, and it calls the filesystem in ROM
when you first boot the Amiga.  So there are already filesystem
handlers (the old ones) controlling the drives.  It is possible to
wrestle control away and make FFS run on floppies, but it's not supported
and also dangerous because FFS can't yet tell when you change floppies,
so its caching (for example) is incorrect.  People who do this, no matter
how careful they are, will eventually trash one of their floppies.

> - Has something been done to make directory access faster, or will the
>  the speedup in this area just be proportional to the speedup for
>  FFS?

The directory access is much faster.

>	Frank Anthes-Harper

Keep in mind I'm only repeating what I read in magazines and in
electronic forums; everything I mentioned was based on a product that
doesn't not exist and may change a hundred times if/before it comes
out.  Don't go building products with this information.	;-)

..Bob
-- 
Bob Page, U of Lowell CS Dept.  page@swan.ulowell.edu  ulowell!page
"What a wonder is USENET; such wholesale production of conjecture from
such a trifling investment in fact."	-- Carl S. Gutekunst