very slow Solaris 10 system with some zones

I've a Sun Fire V240 with Solaris 10 8/07 and 7 zones. The system worked
smooth during the last time.
Last week I was on vacation. On returning a colleague claimed about a slow
server ( a zone on the system ).
The investigation with prstat, mpstat, vmstat on the global zone didn't reveal
any much work.

CPU's were about 90% idle, no paging....

But listening directories and so on where very slow. Also some ssh logins
timed out.

Logging in via the LOM on the console, showed from time to time some processes in the zones, which can't grow their stack because of missing
swap space.

After looking into /zones/*/root/tmp, I've found that there were a lot of files in
tmp.

After cleaning up each zones /tmp the system came back to the usual performance and the colleague was happy again.

This is a fact many people miss when using solaris, that /tmp is located in the
virtual memory.

So do not store large files in /tmp. They are lost in case of a reboot.