Limitations and restrictions for IBM i client logical partitions

Hardware and software prerequisites

For more information about the supported operating systems, see System software maps.

I/O, storage, and networking limitations for virtual Small Computer Serial Interface (SCSI) adapters

• The IBM i 7.1 TR8, or later client logical partitions can have up to 32 disk units (logical volumes, physical volumes, or files) and up to 16 optical units under a single virtual adapter.
• The maximum virtual disk size is 2 TB minus 512 bytes. If you are limited to one adapter and you have a storage requirement of 32 TB, for example, you might need to make your virtual disks the maximum size of 2 TB. However, in general, consider spreading the storage over multiple virtual disks with smaller capacities. This can help improve concurrency.
• Mirroring and multipath through up to 8 Virtual I/O Server partitions is the redundancy option for client logical partitions. However, you also can use multipathing and RAID on the Virtual I/O Server for redundancy.
• It is required that you assign the tape device to its own Virtual I/O Server adapter, as tape devices often send large amounts of data, which might affect the performance of any other device on the adapter.

SAS adapter performance considerations

If you are using the Virtual I/O Server with Peripheral Component Interconnect Express (PCIe) attached serial-attached SCSI (SAS) adapters to virtualize storage with the IBM i operating system, be aware of specific configuration options that maximize performance. Failure to implement these options can cause write performance degradation. Planning for these considerations ensures that the system is sized for the number of IBM i client logical partitions. For more information about how to configure your Virtual I/O Server, see the SAS Adapter Performance Boost with VIOS topic in the IBM developerWorks website.

Virtual Fibre Channel limitations

• The IBM i client partition supports up to 128 target port connections per virtual fibre channel adapter.
• The IBM i 7.2 TR7 and IBM i 7.3 TR3 client partitions support up to 127 SCSI devices per virtual Fibre Channel adapter. The 127 SCSI devices can be any combination of disk units or tape libraries. With tape libraries, each control path is counted as a unique SCSI device in addition to a single SCSI device per tape drive.
• For IBM i client partitions, the LUNs of the physical storage connected with NPIV require a storage-specific device driver and do not use the generic virtual SCSI device driver.
• The IBM i client partition supports up to eight multipath connections to a single fibre channel disk unit. Each multipath connection can be made with a virtual Fibre Channel adapter or with Fibre Channel I/O adapter hardware that is assigned to the IBM i partition.
• Each virtual Fibre Channel adapter in an IBM i client partition must connect to a different physical Fibre Channel port. Connecting more than one virtual Fibre Channel adapter in the same client logical partition to a single physical Fibre Channel adapter port in the Virtual I/O Server is not supported.