Re: FFSv1 (UFS1) vs FFSv2 (UFS2)

[Greg Troxel <gdt%lexort.com@localhost>]

tlaronde%polynum.com@localhost writes:

> I was assuming (don't know why) that when newfs(8)'ing a partition with
> more than 1To, the format would be, automatically FFSv2, FFSv1 being
> the default otherwise.

newfs(8) and fsck_ffs(8) explain this, although I can see that it's
slightly hard to follow.   Basically, retrocomputing aside, there is

  - UFS1 level 4, which has a "FFSv2-format superblock"
  - UFS2

There are statements about UFS2 being better for multi-TB filesystems,
but as far as I know UFS1 works fine.

Another issue is that we have support for extended attributes in UFS1,
but not UFS2 (I believe for no good reason, just that it was added in
one place and not the other, but I'm not sure).  This is necessary for
serving glusterfs.

> Dumpfs(8) is a bit confusing since the superblock are said to be FFSv2,
> while the filesystem is identified as FFSv1. So I gather that, having
> not explicitely requested UFS2, it is UFS1 nonetheless.

Yes.  That's what newfs(8) says.

> The question is: is there any problem to have a more than 1To partition
> with FFSv1? Or is FFSv2 "simply" fastest, specially when using newfs,
> and not trying to be smart with cylinders and grouping?

The rotational stuff is gone in UFS1 level 4.  See fsck_ffs(8)

> If the partition is more than 2To, will the FFSv1 be unable to access
> some blocks?

I believe it will be fine.  I have not been seeing reports of this, and
I would think that if there were we would have updated the man page and
adeed a warning/check in newfs.


But overall, it seems that for 2T and up, the standard approach is:

   use UFS1 if you think you want to serve gluster from it, otherwise
   use UFS2

I am unclear on any really compelling arguments for UFS2 vs
UFS1/ffsv2-super-block.