Recently there have been a lot of new developments in the realm of Power Systems IBM i storage options. Historically, IBM i users have gravitated to Internal storage for a variety of reasons. However, some strategic influencers are driving more and more use of external SAN based storage. Those would include, Power HA and backup considerations; Live Partition Mobility, Lower costs (of SAN storage); Improved connection capabilities; and Improved utilization via cloud technologies.
IBM i supports three basic disk attachment methods: 1) Native attach via raid adapters to internal disks or expansion drawers; 2) Native attach via Fiber channel adapters to supported SAN storage, which includes DS8000, SVC, V7000, V5000 and V3700; or 3) VIOS attached storage options.
Some of the Identifying factors that need to be considered when determining which type of disk storage is right for a particular IBM i environment:
- Size of data in the Enterprise - isolating or consolidating?
- I/O Performance required
- Availability and Backup Requirements
- Data Replication options and POWER HA
- Live Partition Mobility Requirements
- Frequency of deploying new partitions or workloads
- Flexibility vs Complexity
The following requirements might indicate that SAN storage is a preferable solution:
1- Consolidation of partitions via virtualization
2- The sharing of limited fiber ports
3- The need for thin provisioning
4- Large disk requirements on smaller servers that might otherwise cause users upgrade to larger servers to support more internal disk.
5- Desire for improved availability and recovery with disk based replication and PowerHA,
6- The need to shorten backup cycles using Flash Copy services.
Old guidelines for SAN storage performance on IBM i OS have pretty much been replaced by a new reality due to increased performance of adapters and back end storage. In many cases SAN storage performance can equal or exceed internal disk performance, depending on configurations. Several years ago this was not the case.
LUN sizing hints and tips for IBM i with direct fiber attach SAN disk:
- On the DS8000 series, LUNS must be defined to provide 520 byte sector support for IBM i
- The requirement for Fiber Channel adapters is driven by the quantity of LUNS and paths available. A maximum of 32 luns is supported per IOP adapter; and a maximum of 64 luns on the IOP-less adapters.
- Minimum LUN size is currently 17.5GB; Maximum is 2.0TB minus 512 bytes
- A minimum of 6 luns is recommended in any ASP where you care about performance; basic guidance says 12 luns per virtual scsi adapter, with a maximum of 16.
The IBM Disk Magic tool can be used to model the size and number of luns required.
IBM i has many new storage options for both internal and external uses. IBM Power Systems and IBM System Storage continue to provide the most integrated and efficient solutions. More Information on these technologies is available here:
- IBM i 7.1 Technical Overview Redbook - http://www.redbooks.ibm.com/redpieces/abstracts/sg247858.html?Open
- IBM i Storage Techdocs - http://www.ibm.com/support/techdocs/atsmastr.nsf/WebIndex/PRS4011