Subject: Re: Filesystem wishes [was: Re: JFS for NetBSD?]
To: Jason Thorpe <email@example.com>
From: Pavel Cahyna <firstname.lastname@example.org>
Date: 03/19/2003 09:10:41
> > While we're making wishes, what about SGI EFS? It's the stuff
> > they use on install CD's, and it's handy to have a box able
> > to read it, and currently it would mean a linux box.
> Isn't EFS just a hacked UFS? I seem to recall that that's basically
> what it is... but I must admit it's been a long time since I cared :-)
In fact, EFS is similar to UFS or ext2fs. The difference is that the
allocation of space is tracked by extents of variable size, instead of
blocks or fragments of fixed size. So, for a very large unfragmented
file, you need only one reference to an extent in the inode,
instead to many references to blocks in the inode and indirect blocks
(as in ffs or ext2fs). Most of the time, indirect blocks (actually
indirect extents, because they can be variable-sized, too) won't be needed.
This is an improvement over classical UFS. Most modern filesystems have
it. (AFAIK at least HPFS (OS/2), XFS, JFS, NTFS .)
Unfortunately, the size of the EFS filesystem is about 8.4 GB maximum
(because some values are 24-bit, not 32 or 64 bit) so it is not suitable
as FFS replacement.