[horde] Memcache server questions

[Steve Devine]

 We are about a month away from full release of our Horde implementation.
Twice we have had hard failures of our session management system.
We are using memcache on a separate server. Its a SunX4100 with 8gigs  
of available ram, we gave memcached 4Gigs to use and it had been  
running fine. Yesterday our Communication manager sent out a huge mass  
mailing inviting people to try the system and after an hour it went  
right in the tank.
We are in the process of getting another machine to run memcached on  
line so we can do failover but this whole thing spooks me a bit.
I have read many times on this list that memcache is the best way to  
handle sessions on a large installation. Is this still the feeling of  
the list?
One of the problems is when the apache server cannot write the session  
it just hangs and the user gets a blank screen. Soon it seems to  
cascade out of control and stopping and restarting the memcache  
process did not seem to help.
If I decide to abandon the memcache server in favor of mysql am I  
heading down the same road? Anyone out there with experience in either  
of these methods care to comment?
Thanks
/sd

Steve Devine
Michigan State University