Specifications
© IBM Copyright, 2012 Version: January 26, 2012
www.ibm.com/support/techdocs 14
Summary of Best Practices for Storage Area Networks
4 Disk Storage
4.1 General topics
One theme which is repeated throughout best practice statements centers on one
word: consistency. And consistency with disk storage systems is very applicable
across many areas of operation. One area which is often overlooked is consistency
of code version among multiple storage systems of the same type. The primary
reasoning for this suggestion is the code level on a storage system is increasing
playing a role in the overall interoperability within the SAN environment.
Multipathing applications, HBA BIOS firmware, device driver levels, certain operating
system and application fixes and/or patches as well as other devices (such as SVC)
are dependent on a valid matrix of code versions which includes the storage system.
In situations where the server may have resources from multiple storage systems,
trying to reduce the size and complexity of the interoperable code matrix is an
important consideration for SAN and server administrators.
Consistency should also be considered with the workload balance on a given
storage system. The individual access ports of a given storage system should have
equal workloads. If a detailed understanding of the workload is not known, then port
fan-out ratios are the determining factor for balanced traffic per port. If workload
characteristics are known, then fan-out ratios are not as useful as the total IO profile
across multiple storage ports.
Maintaining good workload balance across storage system controllers and RAID
arrays is just as important as consistent workloads on the storage system’s ports.
Overloading a controller is possible, so the administrator needs to keep focus on a
controller’s load factor when allocating storage to some device in the SAN.
Similarly, the workload on RAID arrays needs to be balanced for optimal
performance of the storage system. Some general guidance is available when
calculating the abilities of a RAID array and the values are based on the number of
data drives utilized in the RAID array without consideration for any parity drives.
Depending on the rotational speed of the disk drive, the following are good rules of
thumb:
• 7200 RPM: 75 - 100 IOps
• 10000 RPM: 120 - 150 IOps
• 15000 RPM: 165 - 200 IOps
• SSD: 1500 IOps