[Info-vax] Request description of UFS for VMS person

[Bob Eager]

On Wed, 22 Apr 2009 12:23:34 UTC, billg999 at cs.uofs.edu (Bill Gunshannon)
wrote:

> In article <176uZD2KcidF-pn2-EGCxjRCvkpZd at rikki.tavi.co.uk>,
> 	"Bob Eager" <rde42 at spamcop.net> writes:
> > On Wed, 22 Apr 2009 11:51:40 UTC, billg999 at cs.uofs.edu (Bill Gunshannon)
> > wrote:
> > 
> >> In article <gsms0d$dn$3 at naig.caltech.edu>,
> >> 	glen herrmannsfeldt <gah at ugcs.caltech.edu> writes:
> >> > Bill Gunshannon <billg999 at cs.uofs.edu> wrote:
> >> > (snip)
> >> >  
> >> >> Are you saying that the blocks used by a file that has been deleted are
> >> >> not going to be reused?  Assuming a decent file allocation scheme I would
> >> >> expect the freed blocks to be in locations that were likely to be considered
> >> >> prime real estate for the next file that needed space.
> >> > 
> >> > The MS_DOS allocation method seems to be such that the most
> >> > recently allocated blocks are the last to be reused, assuming
> >> > no reboot in the mean time.  As well as I understand it, there
> >> > is a pointer to the last allocated blocks that is incremented
> >> > until it gets to the end, and then starts over from the beginning.
> >> 
> >> And why does an alocation scheme as bad as this not surprise me?
> >> No wonder we spent so much time de-fraging MSDOS.  :-)
> > 
> > It's there to make undelete useful. And that was only on MS-DOS, where 
> > disks were reasonably small.
> 
> Considering that MS never provided an UNDELETE command I doubt that was
> the reason for the allocation scheme they used.  More likely their
> programmers just didn't know any better.

Ah, but originally I don't think it used that algorithm. I'll have to 
test it out...

I was caught out when I set a student exercise with an MS-DOS disk 
image. It turns out that the FreeBSD MS-DOS file system handler uses a 
randomising algorithm...so I couldn't generate repeatable images with 
the same shell script.

-- 
Bob Eager