SAP HANA uses in-memory database technology that allows much faster access to data than was ever possible with hard disk technology on a conventional database – access times of 5 nanoseconds versus 5 milliseconds. SAP HANA customers can also use the same database for real-time analysis and decision-making that is used for transaction processing.
The combination of faster access speeds and better access for analytics has resulted in strong customer demand for SAP HANA. There are already more than 1600 customers using SAP HANA on Power since it became available in 2015.
One of the drawbacks of in-memory databases is the amount of time required to load the data from disk into memory after a restart. In one test with an 8TB data file representing 16TB database, it took only six minutes to shut down SAP HANA, but took over 40 minutes to completely load that database back into memory. Although the system was up and responsive much more quickly, it took a long time for all data to be staged back into memory.
SAP has implemented features such as the Fast Restart Option to reduce the database load time, but system providers have enhancements to help address the problem. Intel introduced Optane DC memory technology where the data in memory is preserved even when powered down. Optane DC is positioned as a new tier of storage between DRAM and flash storage with more capacity at a lower price than DRAM but with less performance. Optane DC memory can deliver very fast restarts of SAP HANA but introduces new operational management complexity associated with adding a fourth tier of storage.
IBM PowerVM Virtual Persistent Memory
In October 2019, IBM announced Virtual Persistent Memory (vPMEM) with PowerVM. Virtual Persistent Memory isn’t a new type of physical memory but is a way to use the PowerVM hypervisor to create persistent memory volumes out of the DRAM that is already installed on the system. vPMEM is included at no additional charge with PowerVM.
The data in memory is persistent as long as the physical Power server is not powered off. By maintaining data persistence across application and partition restarts, it allows customers to leverage fast restart of a workload using persistent memory. An added benefit is that there is no difference in application performance when using vPMEM because the underlying DRAM technology is the same as for the non-persistent memory.
Although vPMEM does not preserve memory across a server power down, most IBM Power customers seldom power off their systems because of the many reliability features that are built into Power hardware. vPMEM provides for fast restart in the vast majority of planned maintenance and unplanned outages without compromising the performance of HANA during normal use.
vPMEM has several prerequisites:
- POWER9 processor-based systems
- Hardware Management Console (HMC) V9R1 M940 or later
- Firmware level FW940 or later
- PowerVM level V3.1.1
- SUSE Linux 15 for SAP Applications 15 Service Pack 1 with latest maintenance updates to bring the kernel up to 4.12.14-197.26-default or later
- SAP HANA 2.0 SPS 03 Revision 35 (2.00.035)
- SAP HANA 2.0 SPS 04 (adds new features for memory management)
- SAP Note 2618154 SAP HANA Persistent Memory – Release Information
- SAP Note 2700084 FAQ: SAP HANA Persistent Memory
- SAP HANA Administration Guide – Administration Guide: Persistent Memory
IBM has provided the following documents:
- “How-to” recipe for configuring vPMEM: How To Linux Device Mapper creation on Persistent Memory device for IBM POWER 9 systems
- Planning and Implementation Guide – SAP HANA and PowerVM Persistent Memory
SUSE has three technical support bulletins that you should review before implementing vPMEM
- TID 7024333 “Activation of multiple namespaces simultaneously may lead to an activation failure”
- TID 7024330 “vPMEM memory backed namespaces configured as a dump target for kdump/fadump takes a long time to save dump files”
- TID 7024300 “Hot plugging/unplugging of pmem memory having a size that is not in multiples of a specific size can lead to kernel panics”
Virtual Persistent Memory is the latest tool in a long line of IBM and SUSE innovations to help customers get the most out of their SAP HANA on Power environments.
You should strongly consider using vPMEM when running SAP HANA on POWER9 systems.