Richard, Is one single cylinder really that much real estate any more in the era of mod27+ DASD? Do you believe what Alan Altmark tells us from the holy mount in Endicott?
---<snip>--- Date: Tue, 8 Jan 2008 13:01:51 -0500 Reply-To: The IBM z/VM Operating System <[email protected]> Sender: The IBM z/VM Operating System <[email protected]> From: Alan Altmark <[EMAIL PROTECTED]> Subject: Re: z/VM 5.2 Absurd System shutdown - PJBR Content-type: text/plain; charset=US-ASCII On Tuesday, 01/08/2008 at 11:54 EST, David Boyes <[EMAIL PROTECTED]> wrote: > The cyl 0 vs 1 discussion is just a safety measure; CP is usually smart > enough not to shoot itself in the head by paging onto the volume label & > allocation bitmap that tells it where it paged stuff...8-) The paging subsystem will page to cyl 0, but it knows to avoid the label and tracks that have "other CP administrative data" on them. In the interest of avoiding problems, however, don't ALLOCATE cyl 0 as anything other than PERM. It's just not worth the risk. "Cylinder zero is PERM and belongs to CP." I tell you three times. Alan Altmark z/VM Development IBM Endicott ---<snip>--- Note: THREE (3) times no less! Anyone hear a cock crowing? Yes, CP's "special parts" of cylinder zero are currently "protected" -- even from page and SPOOL activity. But is one solitary cylinder per pack so important for page per SPOOL space that you care to risk some future code change (or erroneous PTF code change) that un-protects the CP allocation-map, or the dummy (full-pack) VTOC? I just don't find even that small risk worth the small risk. One cylinder is inconsequential (unless it's CP's "special areas"!). Who knows, maybe with the direction towards 'Live Guest Migration' (a much better choice than dead guest migration!), maybe IBM has other plans for cylinder zero? I'll stick with always allocating cylinder zero as PERM (a simple solution for my simple mind), and suggesting such as a z/VM "best practice". But "go ahead, make my day" ... allocate *your* shop's cylinder zeroes as page or SPOOL space as you see fit. If that ever causes a problem (unlikely as it may be), expect to hear my haunting strains of "I told you so!". ;-) Don't make me search for Alan's post again! :-) But just in case, for future searches, arguments: CPFMTXA FORMAT ALLOC BITMAP PAGE CYL 0 CYL0 Cylinder 0 best practices Mike Walter Hewitt Associates Any opinions expressed herein are mine alone and do not necessarily represent the opinions or policies of Hewitt Associates. "Schuh, Richard" <[EMAIL PROTECTED]> Sent by: "The IBM z/VM Operating System" <[email protected]> 11/14/2008 11:39 AM Please respond to "The IBM z/VM Operating System" <[email protected]> To [email protected] cc Subject Re: FW: Risk of Adding a Paging Volume Neither one of those ever caused me any harm, either. It looks like you are relegating Mike's "best practices" statement to the realm of superstition. Regards, Richard Schuh > -----Original Message----- > From: The IBM z/VM Operating System > [mailto:[EMAIL PROTECTED] On Behalf Of Jim Bohnsack > Sent: Friday, November 14, 2008 8:38 AM > To: [email protected] > Subject: Re: FW: Risk of Adding a Paging Volume > > For the same reason that you don't walk under a ladder, > carrying a black cat in the dark of the moon. > Jim > > The information contained in this e-mail and any accompanying documents may contain information that is confidential or otherwise protected from disclosure. If you are not the intended recipient of this message, or if this message has been addressed to you in error, please immediately alert the sender by reply e-mail and then delete this message, including any attachments. Any dissemination, distribution or other use of the contents of this message by anyone other than the intended recipient is strictly prohibited. All messages sent to and from this e-mail address may be monitored as permitted by applicable law and regulations to ensure compliance with our internal policies and to protect our business. E-mails are not secure and cannot be guaranteed to be error free as they can be intercepted, amended, lost or destroyed, or contain viruses. You are deemed to have accepted these risks if you communicate with us by e-mail.
