Followgin up my own porst - I did some investigaing, and this is caused by the security scriots, which are now increasing wired pages a lot. This appears to push normal procsses out into swap until swap fills. Disabling the secuiryt scripts and the system no longer crashes. So, what changes between June last year and now which would make wired pages behave like this ? Am a bit uncomfortable with the fact that upgrading the OS makes a system go from working fine to runnng out of memory, that doesnt seem right. Did the kernel memory allocator for ZFS chnage during the last 9 months (when did it move the UMA?) -pete.