About paging: I know that there has been much discussion here about giving virtual Linux instances too much virtual memory under VM. The issue is that Linux will us all memory for a disk cache. This same problem will occur under VMWare as well. Note that most OSes for x86 do the same caching that Linux does, so they will have the same problem. OSes that I know for sure will have a problem: Linux (of course), UnixWare (all version), SCO Unix (I forget the exact name, and yes SCO has two different and slightly incompatible Unix systems for x86), Solaris (all x86 versions), Windows NT/2000/XP. I am not sure about Windows95, but I think it does not cache.
-----Original Message----- From: Linux on 390 Port [mailto:[EMAIL PROTECTED] Behalf Of Richard Troth Sent: Monday, October 11, 2004 1:53 PM To: [EMAIL PROTECTED] Subject: Re: Linux Questions I was pained around two months back when one of our marketing people made a snide comment about running MVS on VM "if you want your performance to drop". (My words, not hers.) I had to bite my tounge, focus on what we were discussing, and not go into a tirade about SIE. Consider the term "insertion loss". If you have cable television, or if you are a radio hobbyist, you may have heard it before. The "insertion loss" for z/VM is very small, thanks to SIE assist. The "insertion loss" for VMware is much higher, more like it used to be for VM/370, or perhaps worse because the PC-class systems lack that uniform I/O. And VMware is, like Mark said, less "mature" than z/VM. But it REALLY IS A HYPERVISOR. On Mon, 11 Oct 2004, Tom Duerbusch wrote: > VMWare is NOT VM..it is more like LPAR. > You need XX MBs of ram for VMWare. > If you are running something that needed 512MBs to run and you want to > run 4 copies, then your real storage needed would be (512MB *4 + XX > MBs). VMWare can do some paging at a significant impact to performance, > so don't let it. At least they told you that VMware virtual machines *can* be paged. Originally, VMware always let the host OS deal with virtual machine memory. Later, VMware would try to pin-down some host storage specifically for virtual machine use, a little like V=R. I run VMware on my newest box at home and only this past weekend flipped the switch to let guests page. (To me, that's the normal way to run a virtual machine!) VMware does have certain limits. Again, I applaud what VMware (the company, and its architects) have done, especially given what little was done for them by INTeL. I can see, Tom, how you got your impression. But be aware that the reality is that VMware is NOT LPAR. There ARE LPAR-like schemes for PC-class hardware. VMware ain't one of them. > VMWare seemed to be more akin to V=R with perferred guests. Dedicated > scsi adapters, dedicated LAN cards, dedicated .... Someone mis-presented VMware. Many would expect the majority of VMware virtual machines to have virtual disks much like z/VM minidisks. Just like on z/VM, the disk(s) a guest owns can be virtual or attached. Networking too is a lot more like z/VM: "host only" == guest LAN "bridged ethernet" == VSWITCH But your impression is DEAD ON in so far as z/VM and zSeries do a handier job of creating virtual machines. I go back to the "up to a dozen" virtual machines with VMware -vs- "dozens, hundreds, even thousands" of virtual machines with z/VM. Practically, yeah, this is LPAR. -- R; ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390 ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390
