Small disclaimer : i used AIX really little, most of the time migrating stuff off of it
Looks like server B in your case, has more filesystem caching activity going on.
Meaning, if this is some kind of cluster, and you failover a service which is using that filesystem, it's bound you will have slower response until same read patterns occur on serverA filesystem, and are cached to memory.
So, basically, context is required in this case.
What services are running on that server ?
How are those two servers sharing load - are requests hitting both or failover scenarios etc. ?
I mean, what doesn't actually work or works slower on specified server so you need to
investigate the memory ?
Regards
Peasant.