z/VM: CP Planning and Administration - z/VM - IBM

Overviewv Define minidisks for users. Use the MDISK directory control statement todefine a minidisk for a virtual machine. Use the LINK directory control statementto define a link to another user’s minidisk. The virtual machine for which theminidisk is defined is responsible for formatting it. For more information, see“MDISK Directory Control Statement (Device)” on page 513 and “LINK DirectoryControl Statement (Device)” on page 500.Note: CP and the directory program do not prevent you from defining minidisksthat overlap. If you define such overlap, you assume responsibility for dataintegrity. You can use the Directory Maintenance Facility (DirMaint)optional feature of z/VM to assist in managing the directory.v Set up a minidisk so it can be shared with an operating system running onanother processor and with other virtual machines (using reserve/release).For more information, see “Sharing DASD among Multiple Virtual Machines byUsing Virtual Reserve/Release” on page 619.DASD Space Used for Shared File PoolsTo define file pools, you need to estimate how large each file pool will become. Alsodefine one or more virtual machines to be used for file pool service machines. In sodoing, you must decide what the initial DASD storage for the file pool will be.For information on generating a file pool, refer to z/VM: CMS File Pool Planning,Administration, and Operation.ExpandedStorageExpanded Storage is hardware available only on certain processors. It providesanother level of general-purpose storage. Expanded Storage may be dedicated toone or more virtual machines and shared with CP. It can also be used for pagingand minidisk caching. Do the following for Expanded Storage:v Plan a map of Expanded Storage and determine which virtual machines shouldhave access to this resource (see “Mapping Expanded Storage” on page 593).v Use the XSTORE directory statement to attach Expanded Storage to avirtual machine. (You can also do this by using the ATTACH XSTOREcommand.) For information on the XSTORE directory statement, see “XSTOREDirectory Control Statement (General)” on page 585. For information on theATTACH XSTORE command, refer to z/VM: CP Commands and UtilitiesReference.v Use the RETAIN XSTORE command to set aside Expanded Storage forexclusive use by CP (see z/VM: CP Commands and Utilities Reference). Notethat CP determines which portion of Expanded Storage it will use for paging andminidisk caching. Use the RETAIN XSTORE command to override this.v Code the NOMDC operand of the MINIOPT directory statement if you do notwant to use a portion of Expanded Storage as a minidisk cache (see “MINIOPTDirectory Control Statement (Device)” on page 524 and Chapter 19, “ExpandedStorage Planning and Administration,” on page 591). Otherwise, you do not needto code the MINIOPT control statement.Virtual Disks in StorageA virtual disk in storage is the temporary simulation of an FBA minidisk in anaddress space in system storage. Because a virtual disk in storage is not mappedto a real DASD, having a real FBA DASD in the system configuration is notrequired. By avoiding the I/O overhead, virtual disks in storage may be faster to usethan other minidisks.Chapter 1. Planning and Administration Overview 9