On Aug 22, 2006, at 2:07 PM, Manuel Bouyer wrote:
>> 1) How well does NetBSD >=3 support fsck of a dirty FFS file
>> systems that were mounted with the "softdep" option before the  
>> event that
>> made them dirty?
>
> It doesn't support this at all.  Does this exists in FreeBSD yet ?

Since FreeBSD v5, yes:

http://www.mckusick.com/softdep/
http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/ 
configtuning-disk.html#SOFT-UPDATES

Be cautious in that doing an fsck of very large filesystems (in the  
terabyte range) can require a lot of resources for fsck to run,  
whether in the background or foreground, and the system will be under  
a lot of I/O load until that bgfsck completes.

>> 2) How well does NetBSD >=3 support the snapshot functionality?  I  
>> see
>> that there's a kernel option to enable it.  Is it considered  
>> stable and
>> reliable? What opinion do people who have used it have of it?
>
> I'm using it (without softdeps) and didn't encounter major problems
> with it yet. It's used by dump -X in my case.

For the most part, filesystem snapshots have worked pretty well under  
a bunch of cases on FreeBSD; the example of using dump/restore is a  
good one, also for trying to obtain a more consistent file-level  
backup of an active database, and so forth.

However, snapshots are better thought of as the filesystem equivalent  
of using tags within a version control system like CVS or SVN; they  
let you refer to the entire contents of the filesystem as a single  
consistent entity frozen at one point in time.  They are not a  
substitute for keeping real backups on other storage...

Note that there have also been some deadlock issues with softdeps and  
snapshots under FreeBSD (at least), which have generally been  
triggered by extremely low diskspace conditions-- for example, doing  
an installworld where the boot partition is very low on space.

-- 
-Chuck