Re: VM directory entry for shared DASD

[Edward M. Martin]

Title: RE: VM directory entry for shared DASD

Hello David,             I think that your statement is incorrect.  The logic is there for VSAM, but for the SD and DA files you will need the  R/R.   I am thinking about the Share Power files, DTSFILE, and any Sd files that you have.         There were some IBMLINK INFO APARs about these problems.   Ed Martin Aultman Health Foundation 330-588-4723 [EMAIL PROTECTED] ext. 40441 From: The IBM z/VM Operating System [mailto:[EMAIL PROTECTED] On Behalf Of Wakser, David Sent: Wednesday, September 06, 2006 2:30 PM To: IBMVM@LISTSERV.UARK.EDU Subject: Re: VM directory entry for shared DASD   Rob:         Yes, you have actually underscored what I have been saying: except for the volume containing the lock file, no DASD within a single VM image needs MWV specified!         Thanks. David Wakser -----Original Message----- From: Rob van der Heij [mailto:[EMAIL PROTECTED]] Sent: Wednesday, September 06, 2006 2:26 PM To: IBMVM@LISTSERV.UARK.EDU Subject: Re: VM directory entry for shared DASD On 9/6/06, Wakser, David <[EMAIL PROTECTED]> wrote: >         So, if the shared disk does NOT start ay Cyl 0 but at Cyl 1, > the MWV is worthless and I cannot share disks? If you want the VSE guests in this LPAR to use reserve/release, you need MWV to have CP simulate it (that's the *virtual* reserve/release part). The cyl0 is only when it needs to go to the real device so other LPARs can participate. >         I think what I need to understand is: who says CP has to issue > any reserve/release? Does not VSE (via the lock file or some internal > locking > mechanism) handle this? Why does CP need to be involved? The control unit is supposed to acknowledge R/R to provide exclusive access to the volume for more than one channel program. If you would have guest A issue the reserve and then get guest B from the same z/VM image try it, the control unit would grant access because the LPAR already holds a reserve, so the control unit thinks this is fine. What you want is CP to be arbiter and issue the real reserve for the volume as long as one of the guests holds a reserve. >         BTW, there are no LPARS involved here. And the reason why not > all shared packs start on cyl 0 is because we wanted to retain > uniqueness of DASD volids whenever possible. Thus, the VSE DASD starts at REAL CYL. If it's just 1 z/VM LPAR then you have no need for real reserve to be issued because there is nobody outside who can try. And afaik VSE only does the R/R for some disks (like the lock file) and for the other disks there is logic (in the lock file) that protects the datasets (rather than reserve the entire volume anytime you want to write a shared dataset). I hope I did not make it more confusing that it has to be. Rob -- Rob van der Heij Velocity Software, Inc http://velocitysoftware.com/ Confidentiality Note: This e-mail, including any attachment to it, may contain material that is confidential, proprietary, privileged and/or "Protected Health Information," within the meaning of the regulations under the Health Insurance Portability & Accountability Act of 1996. If it is not clear that you are the intended recipient, you are hereby notified that you have received this transmittal in error, and any review, dissemination, distribution or copying of this e-mail, including any attachment to it, is strictly prohibited. If you have received this e-mail in error, please immediately return it to the sender and delete it from your system. Thank you.