Strange behaviour on 4.99.53

[Paul Goyette <paul%whooppee.com@localhost>]

I've actually been seeing this for a while - at least since 4.99.39 ...

Occassionally it seems that disk I/O activity just stalls.  currently 
I've got a dump(8) running on the filesystem that contains /usr/src and 
/usr/obj .  The dump has been running for more than 5 hours now, and it 
making extremely slow progress.  Sometimes the dump takes 9 or 10 hours 
before it finishes!  The hard drive activity light blinks about once a 
second - it should be on solid, since the machine is doing nothing else.

The dump is running under control of /usr/pkg/sysutils/amanda but I 
don't think amanda has anything to do with the problem.  The dump 
command is being piped to gzip(1) and the gzip output is directed to a 
network socket (amanda's 'dumper' is on the other end of the socket and 
writing things to a disk file on a different physical drive).

I've seen similar "stalls" when gzip is trying to uncompress a file 
located on an NFS-mounted file system.

And recently (since installing 4.99.53 yesterday) I'm occassionally 
seeing long waits for pine to access my mailbox - up to 1 minute or more 
in one case.

Has anyone else seen similar behavior?  Any clues on how to track down 
the cause of this slowness?

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