To your first paragraph, Dave, actually, umm, no. The overhead is really small for [X]NTPD on Linux.
I agree that NTP in each Linux is silly. But the evidence suggests that NTPD is the best behaved, smallest footprint, and all decency of the many daemons possessing virtual Linuxen. In my shop, XNTPD was the first background process we whacked. But it became clear that it was the *last* one we really needed to whack. We turned it back on. Running the NTP server is a whole lot better than even a daily 'ntpdate' via CRON. And precise time synch is vital to any multi-node transactional stuff. (NFS is a common example. Dunno how sensitive WAS and the like are to clock skew.) Now ... an 'ntpdate' at guest boot-up would suffice for local apps. (The clock is just that stable.) But we have lots of network relationships to worry about. The spiffy thing about time on System z is that the clock is incredibly stable. (Ticks at the right rate, though may be off by several minutes. It's always off by the same "several minutes" to great precision.) If we could get the underlying clock set really accurately, I suspect we'd still want to run NTP on most guests for validation and consistency. And incidentally, this is a problem in the VMware world too. (Unless they fixed it quite recently.) On Wed, May 21, 2008 at 1:41 PM, dave <[EMAIL PROTECTED]> wrote: > Thanks, Tom, I appreciate it. However, I would prefer not to > have to run NTP clients in each of the Linux images due to > the overhead that can produce. > > I think the point of confusion here is, at least to me, that > the z10 technical overview document seems to imply that STP > will be used to synchronize the time across LPARs and that > PR/SM will (gradually) update the hardware TOD clock in each > LAPR of a system and across systems, so that all of the > hardware clocks are kept in sync. My question is: what > happens if z/VM is running on one of those LPARs and PR/SM, > under the covers, keeps updating z/VM's hardware TOD clock? > > Or am I completely missing the point here about what STP and > NTP client features are supposed to provide? > > DJ > > ----- Original Message Follows ----- > From: Thomas Kern <[EMAIL PROTECTED]> > To: IBMVM@LISTSERV.UARK.EDU > Subject: Re: z/VM, NTP, and the z/10. > Date: Wed, 21 May 2008 11:49:55 -0500 > > > I don't think that IBM has announced the ability for z/VM > > to update its clock on the fly with input from an STP/NTP > > service. SLES10, however, can use an external NTP source > > to update its own clock (separate from the z/VM > > supervisor). I do this because our hobbit server will > > complain (softly but complain) when my z/VM based linux > > systems are 3 seconds different from the network source > > that the hobbit server got its time from. > > > > /Tom Kern > > > > > > On Wed, 21 May 2008 11:44:28 -0500, Dave Jones > > <[EMAIL PROTECTED]> wrote: >A client has just > > installed a z10 system, with the STP server and NTP client > > >support enabled. In one LPAR there is z/OS 1.9 running > > and exploiting an >external time reference to keep it's > > LPAR time accurate. With the new z/10 >STP and NTP client > > functions available, can the time in the z/VM LPAR also > > >be kept in sync with the time in the z/OS LPAR? If so, > > could this also be >used to keep Linux guests' time in > > sync as well? > > > >Many thanks for your *time* in help me understand > > this....:-) > > > >DJ > -- -- R; <><
