Hi,

We just finished to migrate our server.
Informix version was migrating from TC6 to TD4. Windows NT4 SP6 migrate to Windows 2000 SP3. The performances are bad compare to the performances before the migration. (+ 50%!!!).

Server: IBM 440x
CPU: 4
RAM: 4 GB
OS: Windows 2000 Advanced
Informix: TD4

It's always weird when you have a performance degradation after a migratoin. Questions you'd have to ask yourself is:
How did I do the migration? (Export, no data move)
Did I change disk layout? (Raid?)
Did I change parameters? (Onconfig , OS, GLS ?)
Any logged problems? (Informix online.log, event viewer)

try to identify the performance bottleneck.
disk? - onstat -g ioq
CPU? - onstat -g sch
mem? - onstat -p
LRU, cleaning? - onstat -FR
Locks? - onstat -k
...

should give you already some ideas;