running mksnap_ffs

[Willem Jan Withagen]

Doug Ambrisko wrote:
> | > or things can get wedged.  We have some other patches as well that might
> | > be required.  As a hack on a local server we have been using snap shots
> | > to do a "hot" back-up of a data base each morning.  This is based on
> | > 6.x.
> |
> | What do you mean by "get wedged"?  Are you seeing a deadlock, and if
> | so then what are the details?  When you say 6.x, do you mean
> | up-to-date RELENG_6?  There were various snapshot deadlock fixes
> | committed over the past year including some in the past few months.
> 
> The file-system would come to a stop, processes stuck on bio, snap-shots
> not finishing etc.  This was caused by the system running out of usable
> buffers.  The change forces them to be flushed every so often.  This is
> independant of locking.  10 might be to aggresive.  Some scaling of
> nbuf would probably be better.

When I run mksnap_ffs it runs to the point where ANY access to the filesystem 
gives that process a lockup.
Getting the file system back is only thru "hard reboot". Trying to do it the 
gentle way locks the whole system.

I'm refering further testing and trying until I have more time to upgrade to 
6.2-RELEASE and put some of the debug options in the kernel.

On the otherhand is this my main fileserver. So testing too much is sort of 
dangerous, and running a fsck on 1.5T is very tedious.

--WjW