I ntp sync my z/VM Linux guests from an external source. I have no idea what hardware the ntpd server is running, but I assume it's native, dedicated hardware. I run 'ntpdate' via cron every 30 minutes on my z/VM guests, and am only seeing between 1 and 4 ms corrections (randomly) at every interval. For those reasons, I wouldn't run my ntpd on a z/VM guest. Some of the lower quality Chinese mobos I've seen on peecees don't make for good ntpd servers, either. You need a very stable internal clock with very little drift. Ultimately, you want to ntp sync with a server that gets its value either directly or indirectly from tick or tock (.usno.navy.mil) -- that's fed off of the US Naval Observatory's atomic clock.
--Jim-- James S. Tison Senior Software Engineer TPF Laboratory / Architecture IBM Corporation "A bird in hand is safer than one overhead."
