Miscellaneous limits

There are some other IBM® i system limits, such as the number of basic disk pools, the size of a user space, and the size of a message queue.

Table 1. Miscellaneous limits
Miscellaneous limits Value
Maximum system and I/O hardware configurations and capacities Start of change End of change
Minimum load source size
  • DS8000® or virtual disks with VIOS as server: 35 GB for 520-byte sectors
  • SAN Volume Controller (SVC), Storwize®, virtual disks with VIOS VSCSI or IBM i as server: 40 GB (to get 35 GB usable space)
  • Native attached SAS/SCSI (both 520 byte or 4160 byte sectors): 70 GB
Maximum load source size Start of change
  • 4096/4160 block disk: 16 TB minus 1 block
  • 512/520 block disk: 2 TB minus 1 block
End of change
Start of changeMaximum disk sizeEnd of change Start of change
  • 4096/4160 block disk: 16 TB minus 1 block
  • 512/520 block disk: 2 TB minus 1 block
End of change
Maximum number of disk arms that are contained in all of the basic auxiliary storage pools (ASPs 1 - 32), per partition Start of change3 999End of change
Maximum number of disk arms that are contained in all of the independent auxiliary storage pools (iASPs 33 - 255) in all nodes in a cluster Start of change5 999End of change
Minimum number of disk arms that are required for acceptable performance. Start of changeSee IBM Systems Workload Estimator in the Knowledge Center.End of change
Maximum number of active connections to a logical unit or disk unit in an external storage server or Virtual I/O Server environment. 8
Maximum combined number of disk arms and redundant connections to all disk units 35 600
Maximum number of basic user ASPs 31
Maximum number of independent ASPs 223
Maximum number of logical partitions See Logical partitions in the information center.
Maximum database size for Domino® 64 GB
Maximum size of a user space 1 16 773 120 bytes
Maximum size of a user index 2 1 TB
Maximum size of a data queue or a user queue 3 2 GB
Maximum size of a message queue 4 16 MB (approximately 75 000 messages)
Maximum number of new messages of any one message type on a message queue Limited only by size of message queue
Maximum number of program messages that can be created in a job 5 4 294 967 293
Maximum number of records for each version of the history log 10 000 000
Maximum number of unique Volume IDs displayed/printed in Product Activity Log's Removable Media Lifetime Statistics for each Media Option 5000
Maximum number of input fields that can be specified for a display file 256
Maximum total size of concurrently used teraspace address ranges per job Approximately 64 TB
Range of user-defined double-byte characters that can be defined and maintained using the character generator utility (CGU) for Japanese Hexadecimal 6941 through 7FFE
Maximum memory per partition 32 TB
Minimum memory per partition Start of change
  • 2 GB (minimum)
  • 4 GB (recommended)
End of change
Maximum number of processors per partition Start of change
  • POWER8 and POWER8 compatibility mode: 48 SMT8 processor cores. Can be expanded to 96 SMT8 processor cores or to 192 SMT4 capable processor cores with IBM Lab Services arrangement.
  • POWER9 and POWER9 compatibility mode: 48 SMT8 processor cores. Can be expanded to 192 SMT8 processor cores with IBM Lab Services arrangement.
End of change
Maximum number of hardware threads per partition Start of change
  • POWER8 and POWER8 compatibility mode: 768
  • POWER9 and POWER9 compatibility mode: 1 536
End of change
Maximum partition ID 1000
Start of changeMaximum number of virtual SCSI optical devices per virtual SCSI adapterEnd of change 16
Start of changeMaximum number of virtual SCSI tape devices per virtual SCSI adapterEnd of change 4
Maximum number of virtual SCSI disk devices 32
Start of changeMaximum number of active storage volume paths per virtual Fibre Channel connection (NPIV)End of change Start of change127 with 7.4 TR1 or later, otherwise the limit is 64.End of change
Start of changeMaximum number of active storage volume paths per physical Fibre Channel connection (IBM i Native)End of change Start of change127 with 16Gb or faster adapters and 7.4 TR1 or later, otherwise the limit is 64. End of change
Maximum Virtual I/O Server configurations and capacities See Specifications, Limitations, and Restrictions topics under "Planning for the Virtual I/O Server" in the IBM Power Systems Hardware Information Center.
Maximum number of workload capping groups 255
Maximum number of IMGCLG entries in a single IMGCLG 256
Maximum size of a virtual media 1 000 000 MB
Maximum number of virtual tape resources 35
Maximum number of virtual optical resources 35
Maximum number of active (varied on) optical devices 100
Maximum number of drives from a logical tape library can be attached to an IBM i partition 32
Maximum number of drives can be configured in a logical tape library attached to an IBM i partition 256
Maximum number of storage elements in one logical tape library 15 000
Maximum number of data blocks in a single file on tape 4 294 967 295
Notes:
  1. Listed size is the maximum when the machine is allowed to choose the alignment. Absolute maximum size of a user space is 16 776 704 bytes.
  2. To create a 1 TB capable user index when using the QUSCRTUI API, specify a value of 1 for the index size option. Otherwise, the size limit is 4 GB.
  3. The maximum size of a data queue that can be created through the data queue host server is 16 megabytes.
  4. Message queue QSYSOPR is shipped with a message queue full action of *WRAP. When the message queue is full, the oldest informational and answered messages are removed from the message queue to allow space for new messages to be added. If the removing of the informational and answered messages does not provide enough space, then unanswered inquiry messages are removed until there is space to add the new message. The default reply is sent before an unanswered inquiry message is removed. For more information, see the MSGQFULL parameter on the CHGMSGQ command.
  5. If the job has multiple threads, then the limit is the number of messages from all threads combined.
Table 2. Interprocess Communication (IPC) limits
Interprocess Communication (IPC) limits Value
Maximum number of Single UNIX Specification message queues on the system 2 147 483 646
Maximum size of a Single UNIX Specification message queue 16 773 120 bytes
Maximum size of a single message on a Single UNIX Specification message queue 65 535 bytes
Maximum number of semaphore sets on the system 2 147 483 646
Maximum number of semaphores per semaphore set 65 535
Maximum number of shared memory segments that can be created on the system 2 147 483 646
Maximum size of a teraspace shared-memory segment that is created by using the shmget() function 4 294 967 295 bytes
Maximum size of a teraspace shared-memory segment that is created by using the shmget64() function 17 450 452 123 648 bytes
Maximum size of a resizeable teraspace shared-memory segment 268 435 456 bytes
Maximum size of a nonteraspace shared-memory segment 16 776 960 bytes
Maximum size of a resizeable nonteraspace shared-memory segment 16 773 120 bytes