I'm experiencing very weird problem.
Once in several days the server gets frozen for about 6 minutes!!.

I don't think this is deadlock and I'm almost confident that threads are
paused (by GC?),
because there is thread pool based timer which doesn't fire for
the same amount of time (Server uses about 4-5 threads so there are free
threads for timer to fire)

I'm running server on 32 bit .Net 2.0 SP1 on 4 processor computer with 4GB
ram and /3GB switch.
GC runs in server mode.

According to performance counters this freezing coincides with full garbage
collection.
I see no way to provide mininum code example because I have no clue
what the cause is and I have to wait many days to reproduce it.

For 30 seconds before the freezing I observe following values of performance
counters:
    Available memory on server starts diminishing with rate of several
MB/s. (In total 100MB in 30 secs)
    "Virtual bytes" for the server increases in total by 140 MB
    Gen 2, LOH size are almost unchanged
    Processors are loaded by 20%
    "CLR LocksAndThreads\QueueLength" is around 1

During this 6 minutes
   Available memory diminishes with rate of several MB/s ( 1 GB in total)
   "Virtual bytes" remains constant
   Gen 0, 1, 2 Heap size remains constant
   All managed threads of the server consume 0% of processor resources
   Garbage collector threads consume almost no processor resources
   All 4 processors are loaded at less then 4%
   "Memory pages/sec" is about ~20/sec (which is also at this rate when
everything works fine)
   "CLR LocksAndThreads\QueueLength" is 0
   "Bytes Allocated/sec" is 0

Right after this
    Available memory increases by 700MB
    Gen 2 collection counter increases by 1.
    Gen 2 heap size is diminished by 800 Mb
    LOH size remained the same
    % Time in GC is almost 100% with later decreasing to 8%
    All processors become loaded by ~50%
    All managed threads start doing something
    Garbage collector threads also start doing something
    "CLR LocksAndThreads\QueueLength" becomes something around 1

All these makes me suspect that GC pauses threads and waits for something
for 6 minutes
(usually full garbage collection takes several seconds).

What could make GC to wait for so long?
Another question I'm trying to figure out know is what eats unmanaged
memory? Could it be GC?
If it's not GC, can this cause GC to freeze?

I'd appreciate very much if somebody knows what the problem is or has any
ideas how I could remove or identify it.

TIA, Sergey