[ale] What file system for a software RAID array ?

[Danny Cox]

Greg,

On Sat, 2003-07-19 at 19:49, Greg wrote:
> Why do you like XFS ?  I have heard about it, but must confess my ignorance
> about it.  I thought it was just the file system for SGI.  Of course now I
> must investigate it, but I would really like someone's first hand input.

	At the time, XFS was the only established journalling filesystem
available for Linux.  ext3 was still in development, as was reiser. 
IBM's JFS hadn't been introduced yet.

	XFS had the POSIX ACL implementation (although it (the ACL code) wasn't
ported to Linux yet).  That became my first assignment.  It was designed
years ago by SGI to handle their specific requirements: 

	* large filesystems
	* large files
	* efficient (runs at near the raw disk I/O speed)
	* growable
	* POSIX ACLs
	* extended attributes (ACLs are stored in EAs in XFS)

probably the most important bullet point to us at the time was ACLs.  I
later extended the ACLs to include bits for delete, take ownership, and
change permission to allow Samba to set these flags just as if it were a
Winders NTFS.  JT (John Trostel [Hi, JT!]) coded the Samba portion of
the permission manipulation code.  You just don't know how much fun it
is to have full-blown NTFS permissions enabled on your home mountpoint
and try to start X.  Short answer: it doesn't ;-).

	SGI accepted the ACL changes into their codebase, but didn't want the
extended permission code at all (I wonder why? ;-).

	I in particular wanted some form of journalling fs, because until
2.4.21, my system would tend to hang.  I have a 3dfx VooDoo 3000 video
card, and the one game I continue to play is Unreal Tournament.  Upon
exiting, nine times out of ten, the system would hang at that point,
requiring a reboot.  Let me tell you, a sub second mount wherein the log
was replayed and the filesystem "fixed" made a believer out of me. 
Since 2.4.21, someone has apparently fixed the VooDoo hang problem, as
I've not seen it since.  Hurray for our side!

	Also, back in 2000, as a neophyte kernel hacker, hanging the system was
all too easy.  Having all your fs's journalled was a major life-saver
since the box (notebook) you were developing on was also the test bed
:-(.

	Ah, well.  I guess I've rambled on enough for now.  You can find the
white paper about XFS on the oss.sgi.com site.  See
http://oss.sgi.com/projects/xfs/publications.html for various papers. 
The 1993 papers told the beginning history of XFS.

-- 
kernel, n.: A part of an operating system that preserves the
medieval traditions of sorcery and black art.

Danny

_______________________________________________
Ale mailing list
Ale at ale.org
http://www.ale.org/mailman/listinfo/ale