With every new generation of storage systems, more advanced capabilities are provided, that invariably greatly simplify your life – at least according to the announcements. In practice however, these valuable new functions typically also introduce new a new level of complexity. This tends to make performance less predictable and harder to manage.
Looking back at history, it is important to note that RMF reporting was designed in the early days of CKD (think 3330, 3350) and mainly showed the host perspective (74.1). With the introduction of cached controllers, cache hit statistics came along that eventually made it into RMF (74.5). When the IBM ESS was introduced, additional RMF reporting was defined to provide some visibility into the back-end RAID groups and ports (74.8), which is now used by both HDS and IBM.
It is important to note that no substantial changes to RMF have been made since these early developments. Moreover, many of the advanced functions of today’s storage boxes – point-in-time local copies, asynchronous mirroring, thin provisioning and automatic tiering – are not reported on by RMF at all.
Although command line functions can sometimes be used to extract performance data, such ad-hoc methods are not part of the standard measurement routine. They typically won’t be used when you need them the most: when a problem is still developing. That is the only time you can still avoid service impact. Rather these low-level tools are only used after an issue has made it all the way to the application, so they do not provide the proactive management that enterprises are looking for.
Wouldn’t you agree that all relevant information should be part of RMF, such that we could all use it in our daily proactive performance management?
In most cases, the storage system microcode already maintains the necessary information on the advanced functions, but the work to define an interface with RMF has yet to be performed. It is surprising to see storage vendors introducing new functionality without instrumentation, especially given the mainframe legacy of proper manageability.
We believe change only comes when sufficient customers require it from the vendors. We will provide IntelliMagic’s perspective on what you and the industry should be asking of storage vendors in our next blog posts, which will cover specific RMF enhancement recommendations for each of the enterprise storage vendors.
Editor’s note: This is the first in a series of four blogs by Dr. Houtekamer on the status of RMF as a storage performance monitoring tool, based on experience using available instrumentation for IBM DS8000, EMC VMAX, and HDS VSP / HP XP P9500.