tuning to run large (1000+) numbers of null_mounts

[Kris Kennaway]

On Thu, Jan 19, 2006 at 01:55:22AM -0500, Ensel Sharon wrote:
> 
> 
> On Wed, 18 Jan 2006, Kris Kennaway wrote:
> 
> > > hmmm...the cut and paste of that loud warning was from a 6.0-RELEASE man
> > > page ... if I need to be CURRENT to get the updated man page, do I also
> > > need to be CURRENT to get the safe null_mount code itself ?
> > > 
> > > Or is 6.0-RELEASE safe ? (re: null_mount)
> > > 
> > > Thanks a lot.
> > 
> > 6.0-RELEASE is also safe.  I only just removed the warning the other
> > day, but I'll also be merging it to 6.0-STABLE.
> 
> 
> Ok, that is good to know.
> 
> However, I continue to see instability on this system with the 2000+
> null_mounts.  Are there any system tunables / sysctls / kernel
> configurations that I should be studying or experimenting with that are
> relevant to this ?
> 
> Perhaps looking more broadly, are there any tunables related to large
> numbers of mounted filesystems _period_, not just null mounts ?

Not that I know of.  You'll need to proceed down the debugging route I
mentioned.

> For what it is worth, the system also has several mdconfig'd and mounted
> snapshots (more than 5, less than 10).  Further, all of the null mounts
> mount space from within a mounted snapshot into normal filesystem space.  
> With all the snapshots mounted and all the null mounts mounted, I find
> that commencing an rsync from the filesystem that all these exist on locks
> up the machine.  I can still ping it, but it refuses all connections.  It
> requires a power cycle.
> 
> Comments ?

Snapshots are a much more likely cause of system instability than
nullfs mounts, IMO.

Kris

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