An ongoing discussion about SAP infrastructure

TDI Phase 5 – SAPS based sizing bringing better TCO to new and existing Power Systems customers

SAP made a fundamental and incredibly important announcement this week at SAP TechEd in Las Vegas: TDI Phase 5 – SAPS based sizing for HANA workloads.  Since its debut, HANA has been sized based on a strict memory to core ratio determined by SAP based on workloads and platform characteristics, e.g. generation of processor, MHz, interconnect technology, etc.  This might have made some sense in the early days when much was not known about the loads that customers were likely to experience and SAP still had high hopes for enabling all customer employees to become knowledge workers with direct access to analytics.  Over time, with very rare exception, it turned out that CPU loads were far lower than the ratios might have predicted.

I have only run into one customer in the past two years that was able to drive a high utilization of their HANA systems and that was a customer running an x86 BW implementation with an impressively high number of concurrent users at one point in their month.  Most customers have experienced just the opposite, consistently low utilization regardless of technology.

For many customers, especially those running x86 systems, this has not been an issue.  First, it is not a significant departure from what many have experienced for years, even those running VMware.  Second, to compensate for relatively low memory and socket-to-socket bandwidth combined with high latency interconnects, many x86 systems work best with an excess of CPU.  Third, many x86 vendors have focused on HANA appliances which are rarely utilized with virtualization and are therefore often single instance systems.

IBM Power Systems customers, by comparison, have been almost universal in their concern about poor utilization.  These customers have historically driven high utilization, often over 65%.  Power has up to 5 times the memory bandwidth per socket of x86 systems (without compromising reliability) and very wide and parallel interconnect paths with very low latencies.  HANA has never been offered as an appliance on Power Systems, instead being offered only using a Tailored Datacenter Infrastructure (TDI) approach.  As a result, customers view on-premise Power Systems as a sort of utility, i.e. that they should be able to use them as they see fit and drive as much workload through them as possible while maintaining the Service Level Agreements (SLA) that their end users require.  The idea of running a system at 5%, or even 25%, utilization is almost an affront to these customers, but that is what they have experienced with the memory to core restrictions previously in place.

IBM’s virtualization solution, PowerVM, enabled SAP customers to run multiple production workloads (up to 8 on the largest systems) or a mix of production workloads (up to 7) with a shared pool of CPU resources within which an almost unlimited mix of VMs could run including non-prod HANA, application servers, as well as non-SAP and even other OS workloads, e.g. AIX and IBM i.  In this mixed mode, some of the excess CPU resource not used by the production workloads could be utilized by the shared-pool workloads.  This helped drive up utilization somewhat, but not enough for many.

These customers would like to do what they have historically done.  They would like to negotiate response time agreements with their end user departments then size their systems to meet those agreements and resize if they need more capacity or end up with too much capacity.

The newly released TDI Overview document describes the new methodology: SAP HANA quicksizer and SAP HANA sizing reports have been enhanced to provide separate CPU and RAM sizing results in SAPS”.  I was able to verify Quicksizer showing SAPS, but not the sizing reports.  An SAP expert I ran into at TechEd suggested that getting the sizing reports to determine SAPS would be a tall order since they would have to include a database of SAPS capacity for every system on the market as well as number of cores and MHz for each one.  (In a separate blog post, I will share how IBM can help customers to calculate utilized SAPS on existing systems).  Customers are instructed to work with their hardware partner to determine the number of cores required based on the SAPS projected above.  The document goes on to state: The resulting HANA TDI configurations will extend the choice of HANA system sizes; and customers with less CPU intensive workloads may have bigger main memory capacity compared to SAP HANA appliance based solutions using fixed core to memory sizing approach (that’s more geared towards delivery of optimal performance for any type of a workload).”

Using a SAPS based methodology will be a good start and may result in fewer cores required for the same workload as would have been previously calculated based on a memory/core ratio.  Customers that wish to allocate more of less CPU to those workloads will now have this option meaning that even more significant reduction of CPU may be possible.  This will likely result in much more efficient use of CPU resources, more capacity available to other workloads and/or the ability to size systems with less resources to drive down the cost of those systems.  Either way helps drive much better TCO by reducing numbers and sizes of systems with the associated datacenter and personnel costs.

Existing Power customers will undoubtedly be delighted by this news.  Those customers will be able to start experimenting with different core allocations and most will find they are able to decrease their current HANA VM sizes substantially.  With the resources no longer required to support production, other workloads currently implemented on external systems may be consolidated to the newly, right sized, system.  Application servers, central services, Hadoop, HPC, AI, etc. are candidates to be consolidated in this way.

Here is a very simple example:  A hypothetical customer has two production workloads, BW/4HANA and S/4HANA which require 4TB and 3TB respectively.  For each, HA is required as is Dev/Test, Sandbox and QA.  Prior to TDI Phase 5, using Power Systems, the 4TB BW system would require roughly 82-cores due to the 50GB/core ratio and the S/4 workload would require roughly 33 cores due to the 96GB/core ratio.  Including HA and non-prod, the systems might look something like:

TDI Phase 4

Note the relatively small number of cores available in the shared pool (might be less than optimal) and the total number of cores in the system. Some customers may have elected to increase to an even larger system or utilize additional systems as a result.  As this stood, this was already a pretty compelling TCO and consolidation story to customers.

With SAPS based sizing, the BW workload may require only 70 cores and S/4 21 cores (both are guesses based on early sizing examples and proper analysis of the SAP sizing reports and per core SAPS ratings of servers is required to determine actual core requirements).  The resulting architecture could look like:

TDI Phase 5 est

Note the smaller core count in each system.  By switching to this methodology, lower cost CPU sockets may be employed and processor activation costs decreased by 24 cores per system.  But the number of cores in the shared pool remains the same, so still could be improved a bit.

During a landscape session at SAP TechEd in Las Vegas, an SAP expert stated that customers will be responsible for performance and CPU allocation will not be enforced by SAP through HWCCT as had been the case in the past.  This means that customers will be able to determine the number of cores to allocate to their various instances.  It is conceivable that some customers will find that instead of the 70 cores in the above example, 60, 50 or fewer cores may be required for BW with decreased requirements for S/4HANA as well.  Using this approach, a customer choosing this more hypothetical approach might see the following:

TDI Phase 5 hyp

Note how the number of cores in the shared pool have increased substantially allowing for more workloads to be consolidated to these systems, further decreasing costs by eliminating those external systems as well as being able to consolidate more SAN and Network cards, decreasing computer room space and reducing energy/cooling requirements.

A reasonable question is whether these same savings would accrue to an x86 implementation.  The answer is not necessarily.  Yes, fewer cores would also be required, but to take advantage of a similar type of consolidation, VMware must be employed.  And if VMware is used, then a host of caveats must be taken into consideration.  1) overhead, reportedly 12% or more, must be added to the capacity requirements.  2) I/O throughput must be tested to ensure load times, log writes, savepoints, snapshots and backup speeds which are acceptable to the business.  3) limits must be understood, e.g. max memory in a VM is 4TB which means that BW cannot grow by even 1KB. 4) Socket isolation is required as SAP does not permit the sharing of a socket in a HANA production/VMware environment meaning that reducing core requirements may not result in fewer sockets, i.e. this may not eliminate underutilized cores in an Intel/VMware system.  5) Non-prod workloads can’t take advantage of capacity not used by production for several reasons not the least of which is that SAP does not permit sharing of sockets between VM prod and non-prod instances not to mention the reluctance of many customer to mix prod and non-prod using a software hypervisor such as VMware even if SAP permitted this.  Bottom line is that most customers, through an abundance of caution, or actual experience with VMware, choose to place production on bare-metal and non-prod, which does not require the same stack as prod, on VMware.  Workloads which do require the same stack as prod, e.g. QA, also are usually placed on bare-metal.  After closer evaluation, this means that TDI Phase 5 will have limited benefits to x86 customers.

This announcement is the equivalent of finally being allowed to use 5th gear on your car after having been limited to only 4 for a long time.  HANA on IBM Power Systems already had the fastest adoption in recent SAP history with roughly 950 customers selecting HANA on Power in just 2 years. TDI Phase 5 uniquely benefits Power Systems customers which will continue the acceleration of HANA on Power.  Those individuals that recommended or made decisions to select HANA on Power will look like geniuses to their CFOs as they will now get the equivalent of new systems capacity at no cost.


September 29, 2017 - Posted by | Uncategorized | , , , , , , , , , , , ,


  1. On XeonE7v4 half-socket VM placement supported for HANA on vSphere in production

    Comment by kds | October 22, 2017 | Reply

    • Yes, half-socket min and max, or socket granularity, no mix or match between the two types of configs.

      Comment by Alfred Freudenberger | November 8, 2017 | Reply

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