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SubjectRe: Unnecessary seeks on mounted floppies?
On 15 Apr 96 at 11:48, Martin Buck wrote:

> > > to track 0 when reading from mounted floppies?
> >
> > One reason is if your floppy drive is crap or poorly aligned. The head gets
> > tracked back to track 0 to find out where its drifted to.
>
> In the meantime, I've found the real reason (no, my drive is perfectly OK :-)
>
> The DOS-fs does no read-ahead on the FAT. So whenever you read a cluster of
> a file that's located in a yet unread sector of the FAT, the head has to
> move to track 0 to read the next part of the FAT.
>
> I added a really ugly hack that always causes the whole FAT to be read on
> the first access (if the FAT is small enough, i.e. on floppies). This keeps
> the whole FAT in the buffer cache and now I can read a complete disk
> without any unnecessary seeks. But this is definitely not the right
> solution, because other FSs (ext2, for example) seem to have similar
> problems.

I thought in 1.2 the FAT filesystem driver would read-ahead larger
chunks than 1.3>=59 does. This isn't perfect, but even better. I've
noticed slow floppy access on minix filesystems, too (a lot of
seeking). As already stated some time ago, MS-Smartdrive now reads
complete tracks on the floppy; why not Linux? (The floppy controller
has a read-track command, BTW)

>
> Martin

Ulrich


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