Every site that I have been associated with has operated under the premise that, with the exception of full pack minidisks, cylinder zero (0) is ALWAYS allocated PERM, and a one (1) cylinder reserved space minidisk is placed in the directory for each volume in recognition of that fact.
Since at least VM/ESA 2.4.0, and probably significantly earlier, CP does not use the page slots which would be located on cylinder zero (0) track zero (0), see HCPMSACR MACRO for more information, so there is no likelihood of the volume label being overwritten by CP. However, a problem can arise if paging or spooling space is allocated starting on cylinder zero (0), and subsequently that space is reallocated for user minidisks without taking into account the need to allocate a one (1) cylinder placeholder. To my mind, best practices should dictate either (1) page and spool space will ALWAYS be segregated onto volumes used solely for that purpose, or (2) all volumes SHALL be allocated with a permanent one (1) cylinder type(PERM) placeholder at cylinder zero (0). John P. Baker -----Original Message----- From: The IBM z/VM Operating System [mailto:[EMAIL PROTECTED] On Behalf Of Thomas Kern Sent: Tuesday, June 24, 2008 5:35 PM To: IBMVM@LISTSERV.UARK.EDU Subject: Allocating Cyl Zero as Perm (Was: Performance toolkit under zVM 5.3) I have never seen a problem with CP stepping on the Label. I have stepped on it myself and seen other inexperienced people step on it. That is why I always allocate cylinder zero of a VM volume as perm and allocate a one cylinder minidisk owned by VMDASD there. That is the "best practices" guideline that I follow. /Tom Kern
