Jesse 1 Robinson wrote:
We would like to be able to access >65535 device addresses (UCBs) from a single
LPAR via a single IODF. The need is for bringing a new DASD subsystem online while
retaining the old subsystem until all volumes can be copied across. We currently
have spare UCBs available, but not enough to have all old and new devices online
at the same time. Is this possible?
You can have a maximum of 65,280* devices (not quite 64K) in Subchannel
Set 0. There are some things that can be accessed via other SCSs, but
IIRC the exceptions don't allow you to have more than 65,280 primary
devices online concurrently. That includes all devices, of course,
including networking, tape, consoles, and such.
If replication and PAVs are eating into SCS0, you can move the
secondaries to another SCS to "make room" in SCS0 for additional primary
devices. When last I looked, these could be defined in other SCSs:
- PPRC secondary devices
- PAV aliases
- FlashCopy target devices
Perhaps that would free up enough slots in SCS0 for you. (It seems to
work for almost everyone.)
There is a very narrow exception to the above for IPLing from nonzero
subchannel sets for a small number of volumes. (I don't have that list
handy, but IIRC it includes at least the IPL and IODF volumes but not
many more than that.)
* We reserve 256 subchannels in SCS0 for future use.
--
John Eells
IBM Poughkeepsie
[email protected]
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