Sharing DASD

Reserve/release is a function that allows your virtual machine to share a DASD with another virtual machine or with a system running on another processor. For more information about reserve/release, see z/VM: System Operation and z/VM: CP Planning and Administration.

For cross-system link, use the XLINK FORMAT utility to prepare a DASD volume for sharing. XLINK FORMAT initializes the CSE area on the volume: 
xlink format vaddr volid

Where:

vaddr
specifies the virtual address of the device. The device can be one of the following:
  • A full-pack minidisk, defining the entire real volume
  • The real volume attached to you at address vaddr
  • A minidisk defining the cylinder on the volume containing the CSE area
volid
specifies the volume identifier that must match the volume identifier on the device.
Note:
  1. Virtual disks in storage are not supported for cross-system link.
  2. The volume label on the disk is checked and must match the volid.
  3. You must have write access to device vaddr.
  4. It is recommended that you allocate the CSE area as PERM. If the volume is CP-owned, allocate it as PERM space with the CPFORMAT command.
  5. The volume does not need to be reformatted if it has a CSE area with the ECKD format. ECKD format exists if the volume is ECKD capable and was last formatted from a z/VM® release 1.1 or later system.
  6. Before using the stable and exclusive link modes to link to a minidisk that is controlled by cross-system link, the CSE area on the volume where the minidisk is located might need to be reformatted with the XLINK FORMAT command.
The following are responses from XLINK FORMAT: 
HCPXXL2868I XLINK FORMAT volid - CYL=cccc TRK=tt RECL=llll
            RECS=rr SYSTEMS=ss
Where:
volid
identifies the volume of the specified device.
cccc
identifies the cylinder number where the CSE area was formatted.
tt
identifies the track number of the CSE area.
llll
identifies the number of cylinders made available for XLINK use. For CKD devices it is also the length of the XLINK map records.
rr
identifies the number of XLINK records written on the CSE area.
ss
identifies the number of systems that can share this DASD volume.
HCPXXL2860I WARNING!  IMPROPER USE OF THE XLINK FORMAT COMMAND WILL CAUSE
            LOSS OF MINIDISK DATA.  BE SURE THAT VOLSER volid
            IS NOT ON-LINE TO ANY ASSOCIATED SYSTEMS.
 
            CONTINUE?  ENTER YES OR NO.
If you enter YES, the following response is issued: 
HCPXXL2869I CSE XLINK FORMAT COMPLETE
The following response occurs when you enter the XLINK FORMAT command on a system that is not participating in cross-system link: 
HCPXXL2879I CANNOT VERIFY CSE LINK TABLE (HCPSYSTB) WITH CP