Re: FFSv1 (UFS1) vs FFSv2 (UFS2)

[tlaronde%polynum.com@localhost]

Hello,

On Wed, Jul 03, 2019 at 12:21:39PM -0400, Greg Troxel wrote:
> 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.

Thanks for the clarifications.

One main difference is the time to format huge partitions. It takes a
really long time with UFSv1 while it is fast with UFSv2.

In my case, it was beneficial to use (even by chance) UFSv1 since it
is obviously writing/reading more blocks and this serves as a diagnostic
for the health of the device about which I had worries about
(the disk has been replaced so it is not any more serving 24/24,
7/7 data, but I was trying to see if it could serve as a third
level back-up with sporadic writes and no reads---it has almost
exhausted [as far as SMART is explicit] its spare of sectors, but
otherwise seems sound).

Thanks again!
-- 
        Thierry Laronde <tlaronde +AT+ polynum +dot+ com>
                     http://www.kergis.com/
                       http://www.sbfa.fr/
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