We have an overworked server currently running a single SQL Server 2000 instance on physical hardware, and about 40 different apps interact with it on a daily basis. Last year, the RAID controller failed and we had no spare, so IT Support hurriedly migrated it overnight to a copy running on a VMWare Server. While it was on that server everything ran much quicker due to it being a big improvement in spec. However, the biggest app using it had occasional serious errors which never occurred on physical hardware.

Specifically, several times a week it would disconnect batches of users - anywhere from just ten to hundreds at once, and all at the same time. It didn't affect any particular users or PCs or offices - all were affected equally.

The only common thing was the app, which is a VB6 app using ADO 2.8 to connect. The other apps connecting to that virtualised instance of SQL Server seemingly had no problems, although they were (and are) responsible for only a tiny fraction of the work involving this server.

The upshot is that after about two weeks of loving the speed and hating the random mass disconnections (which we were never able to find a cause for), we sadly took the decision to return to physical hardware and the disconnections vanished.

Now we've reached the point where the old server just can't handle all that's being asked of it, and we're intending to migrate everything to 2 or more other servers. The snag is that there's a good chance they'll have to be virtual ones again. Given what happened last time, I'm trying to find out what possible reasons there could be for these mass disconnections. We were running VMWare ESX, but the network is Novell-based. Also, the server had a linked server setup to connect to an Informix server using a known-to-be-buggy ODBC driver, and this is used throughout the day.

Any ideas on the cause(s)?