Page of GC20-1801-10 As Updated Karch 3, 1980 by TNL GN25-0776
Planning Considerations for otherVirtual Machines
Ho wever, since
reserve/release
al ternate pa ths
si tuations when
senseCCi. the hardware reserve/release is simulated when virtual
is being used, the data integrity is preserved when
are defined. The chart below identifies those
theVK/370 control program changes a reserve CCW to a r-- I I Type IReserve/Release,Virtual Reserve ,CCi Comnd, Alternate IExecutes in the,Release Requestedlsent by , I of I Device
Pa th,Hardware (2-4 '(V Added to ,VM/370 to, Support ,Channel Switch) I Mode in MDISK) ,Device I Note I IDedicatedlNot defined, ,DASD or , ITape IDefined I IMinidisk INot defined, I I Not applicable, Not applicable
Notapplicable, Not applicable Yes No
Reserve 1Sense 2
Reserve 1liN ot lil.ad i i es Ye!:; Re serve I , ,------------------------ , I I Not def ined I No No Reserve 3, I 1----------------- I I I Not def inedl No YES Sense , 4, I I -------1 1 ,Defined Not applicable, Not applicable Sense I 5 I 1----------------------- I 11NormalOperation The command is passed unchanged to the hardware. I , 2When the VK/370 system has been generated with alternate path support'
for those devices, it prevents the devices from being reserved.Thisl action causes VK/370 to avoid a possible channel lockout. VM/3701 does not return any indication of this action to the operating system, issuing the CCW command that the device was not reserved. , 3Without the two-channel switch special feature, VM/370 sends
reserve/releaseCCW command unchanged to the hardware. However,
hardware rejects the command and does not reserve the device.
the
the+Before sending the command to the hardware, VM/370 changes the
reserveCCW command to a sense CCW command and places a virtual
reserve on the minidisk. The real device is not reserved. The
virtual reserve prevents other operating systems running under the
sameVM/370 system from accessing the minidisk; however, these same
virtual operating systems may virtually reserve other minidisks
located on the same real volume. Because the two-channel switch
feature is not installed on the channels, only one address path goes
to the device from theVM/370 processor. This path allows V8/370 virtual reserve/release processing to send a sense CCW to the device,
although the reserveCCW command would be rejected by the hardware. 5When alternate paths to a device have been defined (by the ALTCU operand on the RDEVICE macro instruction and the ALTCH operand on the RCTLUNIT macro instruction), VK/370 changes reserve/release CCW commands to sense CCW commands to prevent a possible channel lockout. , Figure 7. Summary of VM/370 Reserve/Release Support
48.2IBM VM/370 Planning and System Generation Guide
Planning Considerations for other
Ho wever, since
reserve/release
al ternate pa ths
si tuations when
sense
is being used, the data integrity is preserved when
are defined. The chart below identifies those
the
Pa th
Not
Reserve 1
Reserve 1
for those devices, it prevents the devices from being reserved.
reserve/release
hardware rejects the command and does not reserve the device.
the
the
reserve
reserve on the minidisk. The real device is not reserved. The
virtual reserve prevents other operating systems running under the
same
virtual operating systems may virtually reserve other minidisks
located on the same real volume. Because the two-channel switch
feature is not installed on the channels, only one address path goes
to the device from the
although the reserve
48.2