Linux on 390 Port <[email protected]> wrote on 02/02/2015 04:19:19 PM:
> From: Alan Altmark/Endicott/IBM@IBMUS > To: [email protected] > Date: 02/02/2015 04:20 PM > Subject: Re: Expanding CMS Mini Disk - DDR or Copyfile? - still > not expanding > Sent by: Linux on 390 Port <[email protected]> > > The protection is in place because of the allocation map. Unlike other > files on the disk, it is in a fixed location since it is written during > FORMAT and its size never changes, as that size is based on the size of > the disk. But if you add more cylinders, you add more blocks. And as you > do that, the allocation map has to grow. But it can't grow. It's > surrounded by other data. > > I have to say, it's kind of fun to lean back in my rocking chair and see > my programmer id in FORMAT (DMSFOR) from back in the mid-80s. :-) > > Alan Altmark > > Senior Managing z/VM and Linux Consultant > Lab Services System z Delivery Practice > IBM Systems & Technology Group > ibm.com/systems/services/labservices > office: 607.429.3323 > mobile; 607.321.7556 > [email protected] > IBM Endicott I have to take exception. The allocation map like the directory is at heart just another file. Changed block(s) in the allocation map get re-written in a different location as part of the safe updating of a minidisk's metadata. It's size, too, is at least partly malleable. Pulling from another of your posts, allocate and format a 200-cylinder minidisk. That's big enough for the allocation map to be larger than one disk block. It will actually occupy 3: two data and one index block to which the directory points. Now recomp the disk to 150 cylinders. The allocation map will now fit in a single block and that's all that gets written. If you later recomp back to 200 cylinders (as you pointed out, that's do-able) the allocation map will grow back to its original size and its directory entry updated accordingly. -- Mike Harding z/VM System Support /sp ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390 ---------------------------------------------------------------------- For more information on Linux on System z, visit http://wiki.linuxvm.org/
