z/VM Support for XIV
Updated: 23 Feb. 2022
The IBM XIV Storage System can now be attached through supported FC switches to z/VM for system use (e.g., paging, spooling, IPL, etc.). This support eliminates the need for z/VM to access XIV devices through the IBM SAN Volume Controller (SVC). This support provides the ability to define system and guest volumes as emulated devices (EDEVICEs) on IBM XIV Storage.
As previously announced, XIV Storage can also be accessed by z/VM guests through guest-attached FCP subchannels. This support requires the guest to provide the applicable FCP multi-path driver.
Required Software Levels
For EDEVICEs, PTFs for APAR VM64708 are required on z/VM V5.4 and V6.1. Also required are PTFs for CP APAR VM64588 (V5.4,V6.1) and ICKDSF APAR PM11220.
Linux SLES10 SP2 (or newer) and RHEL5.2 (or newer) distributions support XIV Storage through guest-attached FCP subchannels.
Required Hardware Levels
XIV code level 10.2.0.A
When configuring a single XIV LUN as an EDEVICE, each associated FCP (source) subchannel should only be configured to one target port (WWPN) of the XIV Storage System. In addition, it is recommended that each (source) FCP subchannel be defined on a different (source) FCP channel path (or CHPID). This will provide for best LUN availability in the event of a link failure.
EDEVICE use recommendations specific to XIV
- Ensure XIV code level is at the minimum level (10.2.0.A). Otherwise, duplicate EDEVICE checking will be falsely tripped and only allow one XIV LUN to be varied on at a time.
- Configure EDEVICE FCP subchannels as stated above under "Restriction" heading.
XIV LUNs configured as EDEVICEs aren't recommended for environments
where a single FCP source path is expected to be saturated (i.e.,
fully utilized). I/O service time will be elongated. The use of
the IBM San Volume Controller (SVC) or IBM DS8000 should be explored
- An example to avoid is XIV LUN EDEVICEs allocated as CP-Owned PAGE space in environments where workloads require large virtual-to-real memory over-commitments (i.e., heavy paging workloads).
General EDEVICE use recommendations
- Apply ICKDSF APAR PM11220 when performing a CPFORMAT of an XIV EDEVICE greater than 999,999 4096-byte pages. Otherwise, a DMSABE141T CMS termination will occur ending ICKDSF. 999,999 4096-byte pages is 3.8GB.
- Some VM functions require a FICON-attached tape drive and will not function in a FCP SCSI-only environment due to lack of SCSI tape support in the CP Hypervisor. Examples of these functions are the CP Stand-alone Dump Utility, backing up DASD images to tape with the CP DASD Dump Restore (DDR) utility, or backing up Saved Segments and Systems with the CP SPXTAPE command.
- Apply VM APAR VM64588 to avoid a 9276 disabled wait state on VM SHUTDOWN.
- The VM install process only allocates 0.90GB of CP-Owned PAGE or SPOL space regardless of the size of each EDEVICE. 0.90GB is 244,140 4096-byte pages. This isn't adequate for most workloads. Use CPFMTXA or ICKDSF to manually allocate the appropriately sized EDEVICEs. The z/VM CP Planning and Administration book provides guidance on determining production storage requirements.
FCP Configuration & Use Resources
- Fibre Channel Protocol for Linux and z/VM on IBM System z Redbook
- Using z/VM in a SCSI Environment Presentation
FCP Performance Resources
- z/VM CP Disk I/O Performance Evaluation
- z/VM Linux Disk I/O Alternatives Evaluation
- z/VM SCSI Performance Improvements Evaluation
- z/VM QDIO Enhanced Buffer State Management Evaluation
Other z/VM I/O Links: