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Re: FileSystem Support (Rieser, JFS, EXT3, et al.)

From: Andrew Clausen
Subject: Re: FileSystem Support (Rieser, JFS, EXT3, et al.)
Date: Sat, 11 Aug 2001 20:15:28 +1000
User-agent: Mutt/1.2.5i

On Sat, Aug 11, 2001 at 02:44:36AM -0700, IT3 Stuart B. Tener, USNR-R wrote:
> Mr. Clausen:
> The ReiserFS resizer does not allow you to do what partition magic 
> does with an ext2 partition. All their utility does is extend the end 
> of a ReiserFS partition, if you make the device bigger.

And shrink, right?

> Secondly, while I am certainly not a developer of this technology, 
> nor an expert into its design, I am curious why you can move the end 
> of a filesystem, and not the beginning?

Because moving the end doesn't require renumbering blocks.
Basically, all file systems record the location of things relative
to the start of the file system.  If the start changes, then you
have to change basically all of the metadata on the filesystem.

Of course, you could do a raw block copy, but if you switch the
power off in the middle... you loose everything.  (Also, it's
very slow)

A well-designed resizer (like my FAT one *grin*) can deal with the
fact that the locations will all change.

> In other words, if you 
> extend, why can you not shrink it?

Extending is much easier than shrinking.  When you extend, all you
have to do is say the file system is bigger, and the extra space is

When shrinking, you have to make that space available first.
(i.e. move portions of files out of-the-way)

> Why is it difficult to move a filesystem? 

It is hard to interface that with a resizer that has been designed
as making incremental changes to an existing file system, rather than
one that "reconstructs" a file system.

Most resizers are incremental... the only exceptions I know of is
the Parted fat resizer, and partition surprise.  I don't know about
Partition Magic.  (I suspect it must be "reconstructive", since it
has to be able to change the cluster size... but I wouldn't know.
I don't have a copy of it)

> I know very little about Linux LVM, but, even if LVM (Logical Volume 
> Manager for Linux) where to relieve the problem of knowing how to 
> resize all the other filesystem types, it does not address the issue 
> of dealing with Windows Filesystem types, nor other filesystems types 
> which are not Linux, and not Windows.

True, but Windows is also going to use a system with the same benefits
of Linux LVM.  (Windows NT4 / 2000 already have it)

i.e. making resize-the-start irrelevant.

> What period of time (if you or someone else can guess or estimate) 
> are we look at for "parted" to have (at minimum) functionality 
> equivalent to Partition Manager 6?

Well, there are things in Partition Magic (that's what you mean)
that don't seem particularly useful, like spliting/merging partitions,
and HPFS resize support.  I don't know much about Partition Magic.

Also, Parted has stuff that Partition Magic doesn't have (AFAIK), like
support for 5 different types of partition tables, and the ability
to exploit Linux's portability.

Competing with PM isn't really an issue... rather, satisfying the
needs of the free software community is (which includes allowing
people to migrate to GNU/Linux easily)

> I am also going to check out the current version of Mandrake's "disk 
> drake" which apparently does a lot of what I need (I was told), so I 
> am going to test it out as well.

Mandrake doesn't really do much that Parted doesn't do.  (pixel
can tell you more!)


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