On Fri, 31 Oct 2008 11:37:40 -0400, Alan Altmark <[EMAIL PROTECTED] > wrote:
>On Thursday, 10/30/2008 at 10:29 EDT, David Kreuter >While I will grant you the "optimization" point, let's not get too carri ed >away. In an LPAR, SIE handles guest I/O only for dedicated OSA and FCP >adapters. All other I/O is virtualized by CP. SIE *does* handle CP's >I/O! > >The emphasis on the use of a virtual switch rather than dedicated OSAs >leaves us with primarily FCP adapters for SCSI. > >But with all that said, as others have pointed out, the word "overhead" >has no meaning. Yes, there is overhead and sometimes, yes, it can be "n ot >insignificant". The question is whether the applications are meeting >their SLAs and whether the IT provider is meeting its expense goals. "C an >I get acceptable application performance at a cost I can afford?" As wa s >mentioned, you may have more overhead handling an I/O request, but if yo u >can satisfy it from MDC, it was time well-spent. Assuming, of course, >you've got the CPU available to handle the I/O request! > >Alan Altmark >z/VM Development >IBM Endicott >======================== ========================= ========== ============== The person who asked the question has been asked to review virtualization options (VMWARE, p- series, and z/VM) and determine which workloads should go where. Since th midrange folks have so far decided "we don't need z/VM, we have VMWARE", this is actually pro gress. Unfortunately, his background is all in PCs and Linux (and i-series), no mainframe. But he really is trying to understand the mainframe. He wants to know if VM is like the VM WARE he is failiar with - - at least he ASKED instaed of making assumptions. I don't think that the word "overhead" has no meaning. I'm pretty sure he meant CPU overhead comparing native to a guest. I think that he has observed or been told th at running Linux guests under VMWARE takes more processor than without VMWARE, and that this incr eases for heavy I/O workloads. I would expect the same thing to be true for z/VM, but I would HOPE that the mainframe does it better. Almost all I/O on a PC is handled by the central processors, whil e the mainframe has the IOPs to do much of that work. It would be nice to quantify this, though. Alan Ackerman Alan (dot) Ackerman (at) Bank of America (dot) com
