By Charles Mari, Advisory programmer, z/OS design/development
A new optional feature of the IBM zEnterprise EC12 (zEC12) processor is support for flash memory (a.k.a. Flash Express). The first exploiter of this flash memory is the z/OS operating system for paging. I am a member of the team responsible for the design, development and testing of this z/OS support. This post and subsequent posts from other members of the team will provide an overview of the support and additional details on various aspects of the project.
The flash memory cards on the zEC12 processor come in pairs with each pair of cards providing 1.4 terabytes of storage. The cable-connected pairs plug into the I/O drawer and up to 4 pairs of cards can be installed. The architectural approach (programming model) for Flash Express, architecturally called storage-class memory (SCM), hides the flash technology and implementation specifics from the user/exploiter.
The z/OS Real Storage Manager (RSM) and Auxiliary Storage Manager (ASM) now utilize this flash memory as another form of auxiliary storage. Auxiliary storage is used when pages of data need to be moved out of real storage due to real storage usage requirements, or when applications/components explicitly request to move some pages out of real storage. Prior to Flash Express, paging data sets on Direct Access Storage Devices (DASD) were the only storage medium available for auxiliary storage. Users may now optionally request that Flash Express be used in conjunction with traditional paging data sets to form the 'pool' of auxiliary storage. RSM and ASM decide where a page of data should be written (DASD or flash) based on factors such as space availability and the characteristics of the data being written. ASM access data on Flash Express (reads and writes) via the STARTIO interface.
This new z/OS support is provided via an SMP/E installable web-deliverable available from the z/OS download website - see 'RSM Enablement Offering for z/OS R13'.
Flash Express' fast I/O rates and low I/O latency times provides benefits in the following areas/functions:
Improves the handling of unplanned paging workload spikes
Reduces system performance slowdowns that can occur during workload transitions when data needs to be brought into real storage from auxiliary storage
Lessens the impact to the system during diagnostic data gathering by reducing SVC dump capture times.
Another benefit of Flash Express is the enablement of pageable large (1MB) pages. Prior to Flash Express, 1MB pages were fixed in real storage (i.e. never paged-out to auxiliary storage) and usage was limited to a few exploiters. By allowing 1MB pages to be pageable, use of 1MB pages is now available to a wider
range of applications and users.
Performance scenarios developed and executed by the z/OS performance analysis team have provided data that supports the above-mentioned Flash Express benefits. For example, in a CICS transaction environment simulating a workload transition situation (where a large amount of data must be paged-in from auxiliary storage before a steady-state transaction rate is achieved) the steady-state is achieved significantly faster with Flash Express vs. a non-Flash Express environment.
The past few months leading up to general availability of the RSM Enablement Offering has been a very busy time for the team involved in the development of Flash Express and pageable large pages. The completion of internal system testing and early support programs at several internal and external customers has been our main focus during this time. Flash Express and pageable large pages will play a key role in the success of the zEC12 processor. The team is committed to ensuring this success.
This blog post is part one of a four part series on FlashExpress from the Flash development team. Check out other posts on the Mainframe Insights blog:
Charles Mari is an advisory programmer in z/OS design/development. He has 31 years of experience in z/OS Storage Management (ASM, RSM, VSM) and JES.