On Thu, Jul 1, 2010 at 1:53 AM, Martin, Terry R. (CMS/CTR) (CTR) <terry.mar...@cms.hhs.gov> wrote:
> Anyway, during our z/Linux guest build process, which we are doing at a very > fast pace, we end up initializing the z/Linux DASD under z/VM. Now, when we > execute the z/Linux Kick Start that process comes right back and initializes > the same DASD. This process depending on the amount of DASD being presented > to the guest can take two or more hours to complete with the majority of the > time being spent on the DASD initialization phase of the Kick Start. As Hans points out, it has considerable systems management advantages to leave the real volser to CP. Some of the claimed performance benefits of dedicated DASD seems to build on hearsay, ancient VM releases, wishful thinking and fading memory :-) But you can save yourself some time by not initializing the volume on z/VM first. For volumes that only contain mini disks, it's enough to format cylinder 0 only and put a label on (the RANGE option in ICKDSF). The virtual machine will need to format the mini disk anyway. The recommendation to do it twice (just in case) stems from a Linux bug that was fixed 8 years ago. Just remember that for page and spool packs, you *do* have to format the full volume. In the early days, Linux' dasdfmt also had the option to format only part of the minidisk. This option was removed because some people misused it and then reported a problem when the disk was not formatted. Since you can't prevent Linux from formatting, the alternative is to skip the formatting on z/VM (as explained above). If your DASD subsystem has magic duplication features (snapshot, flashcopy, etc) you can skip both steps. To do that, you once prepare a disk with dasdmft (and maybe even mkefs2) and use that as the source to flash over a fresh volume when you need a Linux disk. If supported, you can just flash the large mini disk. Otherwise, you flash the entire volume and use ICKDSF to relabel the real volume (that does not touch the mini disk at cylinder 1). That's where it helps to let each Linux have the same virtual volser for the disk. Rob
