SAPonPower

An ongoing discussion about SAP infrastructure

SAP increases support for HANA on Power, now up to 16 concurrent production VMs with IBM PowerVM

On March 1, 2019, SAP updated SAP Note 2230704 – SAP HANA on IBM Power Systems with multiple – LPARs per physical host.  Previously, up to 8 concurrent HANA production VMs could be supported on the Power E880 system with 16 sockets.  Now, the new POWER9 based E980, also with 16 sockets, is supported with up to 16 concurrent HANA production VMs.  As was the case prior to this update, each VM must have a minimum of 4 cores and 128GB and can grow to as large as 16TB for OLAP and 24TB for OLTP.  The maximum VM count may be reduced by 1 if a shared pool is desired for one or more non-production HANA, any other SAP or non-SAP workloads. There is no restriction on the number of VMs that can run in a shared pool from an SAP perspective, but practical physical limits are usually hit before any PowerVM architectural limits. CPU capacity not used by the production VMs may be shared, temporarily, with VMs in the shared pool using a proprietary technology called dedicated-donating where the production VM, which owns the CPU capacity, may loan part of it to the shared pool and get it back immediately when needed for that production workload.

Most customers were quite happy with 8 concurrent VMs, so why should anyone care about 16?  Turns out, some customers have really complex landscapes.  I recently had discussions with a customer that has around 12 current and planned production HANA instances. They were debating whether to use HANA in a multi-tenant configuration.  The problem is that all HANA tenants in a mult-tenant VM are tightly bound, i.e. when the VM, OS or SAP software needs to be updated or reconfigured, all tenants are affected simultaneously.  While not impossible to deal with, this introduces operational complexity.  If those same 12 instances were placed on a new POWER server, the operational complexity could be eliminated.

As much as this might benefit the edge customers with a large number of instances, it will really benefit cloud vendors that utilize Power with greater flexibility, more sharing of resources and lower management and infrastructure costs.  Also, isolation between cloud clients are essential, so multi-tenancy is rarely an effective option. On the other hand, PowerVM offers very strong isolation, so this offers an excellent option for cloud providers even when different clients share the same infrastructure.

This announcement also closes a perceived gap where VMware could already run up to 16 concurrent VMs on an 8-socket system.  The caveat to that support was that the minimum and maximum size of each VM when running at the 16 VM level was ½ socket.  Of course, you could play the mix and match game with some VMs at the ½ socket level and others at the full or multi-socket level, but neither of these options provides for very good granularity.  For systems with 28-core sockets, the granularity per VM is 14 cores, 28 cores and then multiples of 28 cores up to 112 cores.  For those that are configured at 1/2 sockets, if there is no other workload to consume the other 1/2 socket, then the capacity is simply wasted.  Memory, likewise, has some granularity limitations.  According to VMware’s Best Practice Guide, “When an SAP HANA VM needs to be larger than a single NUMA node, allocate all resource of this NUMA node; and to maintain a high CPU cache hit ratio, never share a NUMA node for production use cases with other workloads. Also, avoid allocation of more memory than a single NUMA node has connected to it because this would force it to access memory that is not local to the SAP HANA processes scheduled on the NUMA node.”  In other words, any memory not consumed by the HANA VM(s) on a particular socket/node is simply wasted since other nodes should not utilize memory across nodes.

By comparison, production HANA workloads running on PowerVM may be adjusted by 1 core at a time with memory granularity measured in MB, not GB or TB.

In an upcoming blog post, I will give some practical examples of landscapes and how PowerVM and VMware virtualization would utilize resources.

With this enhanced level of support from SAP, IBM Power Systems with PowerVM is once again the clear leader in terms of virtualization for HANA environments.

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March 11, 2019 Posted by | Uncategorized | , , , , , , , | Leave a comment