Little UFS2 FAQ

Wed Apr 23 13:29:56 PDT 2003

Hi,

Great work on this FAQ. For some time that I'm looking for a faq like
this.

I searching for such a FAQ related to SCHED_4BSD and SCHED_ULE
schedulers for people who just understand funcionality.

It is possible to create a faq about this subject?

Thanks very much,

		Nuno Teixeira

On Wed, Apr 23, 2003 at 03:20:47PM +0200, Jeroen C. van Gelderen wrote:
> Little UFS2 FAQ (20023/04/23), culled from contributions by:
> 
> Peter Schultz <peter at jocose.org>
> "Poul-Henning Kamp" <phk at phk.freebsd.dk>
> Marcin Dalecki <mdcki at gmx.net>
> CARTER Anthony <a.carter at cordis.lu>
> Robert Watson <rwatson at freebsd.org>
> Terry Lambert <tlambert2 at mindspring.com>
> Frank van der Linden <fvdl at wasabisystems.com>
> Manfred Antar <null at pozo.com>
> Narvi <narvi at haldjas.folklore.ee>
> Takahashi Yoshihiro <nyan at jp.FreeBSD.org>
> Alexander Pohoyda <alexander.pohoyda at gmx.net>
> Bruce Evans <bde at zeta.org.au>
> "Wilkinson,Alex" <Alex.Wilkinson at dsto.defence.gov.au>
> 
> 
> 
> What is UFS1?
> 
> The long-time BSD(?) native filesystem.
> 
> 
> 
> What is UFS2?
> 
> UFS2 is an extension to the well-known UFS. It adds 64 bit block 
> pointers (breaking the 1T barrier), support for extended file storage, 
> and a few other things.
> 
> Short summary of changes:
>  o 64-bit pointers up the wazoo
>    (implies that inodes have doubled in size, and now are 256 bytes)
>  o Layout and functional changes to help support variable-size blocks
>    (extent-like allocation)
>  o Extension of various flag fields
>  o Addition of per-inode extended attribute extent
>  o Lazy inode initialization (watch newfs(8) fly)
> 
> Apart from these modifications all UFS1 code is being used in UFS2 
> unchanged.
> 
> 
> 
> What is the difference between UFS and FFS?
> 
> UFS (and UFS2) define on-disk data layout. FFS sits on top of UFS (1 or 
> 2) and provides directory structure information, etc, etc. This FAQ is 
> about a revision of UFS named UFS2.
> 
> 
> 
> What is the rationale for UFS2?
> 
> The motivating factor in the layout change was the need for better 
> Extended Attribute (EA) support, and while the developers were at it 
> they figured they'd do a bunch of other useful things too.  UFS2 uses 
> the same basic technologies as modern UFS1 (inodes, linear directory 
> layout, soft updates, snapshotting, background file system checking, 
> etc) so it was a relatively low-risk change.
> 
> 
> 
> Why did you not add <feature> while you were at it?
> 
> It would most likely require significant changes whereas the developers 
> wanted to restrict themselves to low-risk modifications only. See 
> previous question.
> 
> 
> 
> Which OSes support UFS2?
> 
> FreeBSD and NetBSD. (Others?)
> 
> 
> 
> What is the UFS2 status on FreeBSD?
> 
> As of 2003/04/20, newfs(8) and sysinstall(8) will create UFS2 file 
> systems by default, unless explicitly specified.  Users wanting to 
> create UFS1 file systems for whatever reason (interoperability with 
> earlier versions, etc) should be sure to employ the -O1 flag to 
> newfs(8), or hit '1' in the label editor in sysinstall(8) to select 
> UFS1.
> 
> 
> 
> What is the UFS2 status on NetBSD?
> 
> As of 2003/04/02 UFS2 is not (yet) the default type for FFS 
> filesystems. newfs(8) will create a normal FFS filesystem by default. 
> If you want an UFS2 fileystem, specify "-O 2" as an option.
> 
> No additional kernel options are needed for UFS2 support, it's 
> contained within the FFS code.
> 
> Please note that older fsck binaries will complain a bit about 
> filesystems if you boot a new kernel, because of some superblock 
> changes. This is harmless. However, if you have 1.6 fsck binaries, they 
> will signal a fatal superblock mismatch with the first alternate, 
> because they compare too many fields (even ones that aren't useful). 
> This is annoying, and I'd advise peole to upgrade their fsck_ffs binary 
> before using a new kernel. 1.6.1 will have an fsck that is forward 
> compatible. Again, none of this signals actual filesystem damage, but 
> it's still annoying.
> 
> 
> 
> Does the /boot/loader now understand UFS2 on the root filesystem (i386)?
> 
> Yes, modulo the restriction that your root filesystem cannot be larger 
> than 1.5TB. David Schultz et al. proposed a patch to remove this 
> limitation.
> 
> 
> 
> Does the /boot/loader now understand UFS2 on the root filesystem (PC98)?
> 
> Nope. It is unknown if work is underway to address this.
> 
> 
> 
> Is there a UFS to UFS2 conversion tool?
> 
> No. You can however dump/restore from UFS to UFS2.
> 
> 
> 
> Will "dump" on UFS and "restore" on UFS2 filesystem work?
> 
> Yes, that will work.
> 
> 
> 
> Does UFS2 dynamically allocate inodes?
> 
> No it does not.  Inodes are preallocated, but UFS2 lazily initializes 
> them.  This mainly means that newfs(8) runs much faster.
> 
> 
> 
> Does Grub work with UFS2?
> 
> No. Not yet(?).
> 
> 
> -- 
> Jeroen C. van Gelderen - jeroen at vangelderen.org
> 
> "They accused us of suppressing freedom of expression.
> This was a lie and we could not let them publish it."
>   -- Nelba Blandon,
>      Nicaraguan Interior Ministry Director of Censorship
> 
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