mkdosfs

heavytull · External Since: Apr 05, 2006 Posts: 214

I'm trying to make a dos fs (fat32) with the mkdosfs;
but i don't understand what is the -f option for!
the man mkdosfs says it is for specifying the number of fat; and it is
by default 2;
what is the number of fat??

Peter Jensen · External Since: Sep 12, 2004 Posts: 492

heavytull wrote:

> I'm trying to make a dos fs (fat32) with the mkdosfs; but i don't
> understand what is the -f option for! the man mkdosfs says it is for
> specifying the number of fat; and it is by default 2; what is the
> number of fat??

Well, as the manual points out, it's the number of File Allocation
Tables. Traditionally, there was two copies of the table, so that some
errors could possibly be detected and maybe even corrected. I'm not
aware of any OS that handles more than two, and using only one would not
buy you much extra space, and will remove what little fault detection is
present. Therefore it is a rather pointless option, if you ask me.
Just leave it at the default.

--
PeKaJe

The decision doesn't have to be logical; it was unanimous.

heavytull · External Since: Apr 05, 2006 Posts: 214

Peter Jensen wrote:
> heavytull wrote:
>
> > I'm trying to make a dos fs (fat32) with the mkdosfs; but i don't
> > understand what is the -f option for! the man mkdosfs says it is for
> > specifying the number of fat; and it is by default 2; what is the
> > number of fat??
>
> Well, as the manual points out, it's the number of File Allocation
> Tables. Traditionally, there was two copies of the table, so that some
> errors could possibly be detected and maybe even corrected. I'm not
> aware of any OS that handles more than two, and using only one would not
> buy you much extra space, and will remove what little fault detection is
> present. Therefore it is a rather pointless option, if you ask me.
> Just leave it at the default.
>
you mean using only one fat wouldn't save me that space? even windows
formatting tool makes 2 fat's?
anyway, thanks for your info, i can now go head;
Wink

Michael B. Trausch · External Since: Apr 23, 2006 Posts: 156

heavytull wrote in <1147355694.152893.133150 DeleteThis @q12g2000cwa.googlegroups.com>
on Thu May 11 2006 09:54:
>
> you mean using only one fat wouldn't save me that space? even windows
> formatting tool makes 2 fat's?
> anyway, thanks for your info, i can now go head;
> Wink

>

The number of FATs present on the disk, per the specification, can be any
number. This number is stored in the BPB on an FAT filesystem.

However, most operating system drivers that read and write the FAT
filesystem probably won't make use of more then two, and many may not know
what to do in the event that there is less then two. Moreover, one of the
ways that a disk checking program such as CHKDSK on DOS attempts to
review/detect/check the system is by comparing copy 1 of the FAT to copy 2
of the FAT, and see if there are any differences. If so, it attempts to
investigate them to see what caused the errors, etc.

It really is about the only feature of FAT that is used for error checking.
FAT is not a very well designed filesystem, IMHO, mostly because it is
painstakingly simple and doesn't have lots of checks and balances within
the filesystem itself.

As a general rule, unless you know the details of the filesystem
implementation and you know what you're doing, it is best to not mess
around with the parameters of the filesystem. Just let the defaults work
for you -- the defaults are the defaults for a reason.

- Mike

Peter Jensen · External Since: Sep 12, 2004 Posts: 492

heavytull wrote:

> you mean using only one fat wouldn't save me that space?

It would at best be a marginal saving, and usually not worth it. If
your disk size is counted in MB or more, I doubt the number of FATs
matter much in the grand scheme of things.

> even windows formatting tool makes 2 fat's?

I believe that this is the standard, yes.

> anyway, thanks for your info, i can now go head; Wink

Good luck (you'll need it to maintain data integrity on a FAT-based file
system Smile

).

--
PeKaJe
He left the unspoken question hanging in the air. How /did/ one
annoy a two-kilometer-long black rectangular slab? And just
what form would its disapproval take? -- 2010, Arthur C. Clarke