Best way to connect multiple switches together

We currently have five 24 port 3com unmanaged switches. Four of them are 100Mb switches with no gigabit port (MDI Uplink port is 100Mb). The fifth is a full gigabit switch which we use for all of our servers. They are daisy chained together at the moment, kind of like this:

At certain times of the day, network performance becomes atrocious. We've verified that this has nothing to do with server capacity, so we're left with considering network I/O bottlenecks. We were hoping to connect each 100Mb switch directly to the gigabit switch so that each user would only be 1 switch away from the server ... like this:

The moment this was connected, all network traffic stopped. Is this the wrong way to do it? We verified that no loops exist, and verified that we didn't have any crossover cables (all switches have Auto-MDI). Power cycling the 5 switches didn't do anything either.

Maybe the switches were just in awe of your amazing topology?

Seriously though, if you can take the time, do it again, but only connect one switch at a time to the Gb switch, and verify connectivity and function at each step.

When the network finally halts, disconnect all of the switches, and try connecting that switch first. If it does it again, disconnect everything on that switch and add them back, one by one to find the unhappy link.

If it doesn't die, add switches until it does. If it fails after adding more switches, maybe one of the switches can't handle the size of the MAC address table, and you need a bigger switch?

I'd definitely try to get the latter topology working (with Matt Simmons' diagnostic hints as a guide), as it will provide better latency (always only one hop away). Also, given your very limited interconnect capacity, try to:

• put machines which often talk to each other on the same switch (so that the interconnects don't have to carry as much traffic); and
• hook machines that have gigabit NICs and talk to a lot of other machines on the gigabit switch directly (so they can get their data into the network as efficiently as possible).

Ultimately, though, you can't stick a ten pound turkey in a five pound bag, and I'd be writing up a plan for purchasing a set of managed gigabit switches, based on your description of the network being heavily utilised already.