SAPonPower

An ongoing discussion about SAP infrastructure

POWER10 – Memory Sharing and how HANA customers will benefit

As an in-memory database, SAP HANA is obviously limited by access to memory.  Having massive CPU throughput with a small amount of memory could be useful for a an HPC application that needs to crunch through trillions of operations on a small amount of data. By comparison, a HANA system typically scales up with both CPU and memory at the same time.

Intel attempted to solve this problem through the use of large scale persistent DIMMs.  Unfortunately, they delivered a completely unbalanced solution with their Cascade Lake processors that included a small incremental performance increase coupled with Optane DIMMs which are 3 to 5 times slower than DDR4 DIMMs (at best).  By the way, the new “Barlow Pass” Optane DIMMs, that will be available with next gen Copper Lake and Ice Lake systems, will reportedly only deliver 15% bandwidth improvement over today’s “Apache Pass” DIMMs.[i]  Allow me to clap with one hand at that yawner of an improvement.  Their solution is somewhat analogous to a transportation problem where a road has 2 lanes and is out of capacity.  You can increase the horsepower of each vehicle a bit and pack in far more seats in each vehicle, but it will likely to take longer to get all of the various passengers in different vehicles to their destination and they will most assuredly be much more uncomfortable.

IBM with POWER10, but comparison, attacked this problem by addressing all aspects simultaneously.  As mentioned in part 1, POWER10 sockets have the potential of delivering 3 times the workload of POWER9 sockets.  So, not a small incremental improvement as with Cascade Lake, but a massive one.  Then they increased the bandwidth to memory by at least 4x, meaning they can keep the CPUs fed with data … and in case memory can’t keep up, they added support for DDR5 and its much faster speeds and throughput.  Then they increased socket to socket communications bandwidth by a factor of four since transactional and analytic workloads, like HANA, tend to be spread across sockets and often need to access data from another socket.  And just in case the system runs out of DIMM sockets, they introduced a new capability, “memory clustering” or “memory inception”[ii] which allows memory on another physical system to be accessed remotely (more on this later) with a 50 to 100ns latency hit[iii].  And just to make sure that I/O did not become the next bottleneck, they have doubled down on their previous leadership with being the first major vendor to support PCIe Gen4 by including support for PCIe Gen5 with a potential for twice the I/O throughput.

Using the previous analogy, IBM attacked the problem by tripling the horsepower of each vehicle with lots of extra doors and comfortable seats, quadrupling the number of lanes on the road and enabled each vehicle to support tandem additions.  In other words, everybody can get to their destinations much faster and in great comfort.

So, what is this memory clustering?  Put simply, it is an IBM developed technology which enables a VM on one system to map memory allocated to it by PowerVM on another system as if it was locally attached.  In this way, a VM which requires more memory than is available on the system upon which it is running can be provided with that memory from one or more systems in the cluster.  It does this through the same PowerAXON (IBM’s SMP interconnect technology) as is used within each system across sockets.  As a result, the projected additional latency is likely to be only slightly higher than accessing memory across the NUMA fabric.

IBM described multiple different potential topologies, ranging from “Enterprise Class” at extreme bandwidth, to hub and spoke; mixing and matching CPU heavy with Memory heavy nodes to even multi-hop pod-level clustering of potentially thousands of nodes.  With POWER10 featuring a 2 Petabyte memory addressability, the possibilities are mind boggling.

For HANA workloads, I see a range of possibilities.  The idea that a customer could extend memory across systems is the utopia of “never having to say I’m sorry”.  By that, I mean that in the bad old days (current times that is), if you purchased, for example, a 2TB system with all DIMM slots used, and your HANA instance needed a tiny amount more memory than available on the system, you had three choices: 1) let HANA deal with insufficient memory and start moving columns in and out of memory with all of the associated performance impact implied, 2) move the workload to a larger system at a substantial cost and a loss of the existing investment (which always brings a smile and hug from the CFO) or 3) if possible, shut down the instance and the system, rip out all existing DIMMs and replace them with larger ones (even more disruptive and still very expensive).

With memory clustering, you could harvest unused capacity in your cluster at no incremental cost.  Or, if all memory was in use, you could resize a less important workload, e.g. a HANA sandbox VM or non-prod app server, and reallocate it to the production VM requiring more memory.  Or you could move a less important workload to a different server potentially in a different data center or perhaps a much smaller system and reuse the memory using clustering.  Or you could purchase a small, low GHz, small number of activated cores system to add to the cluster with plenty of available memory to be used by the various VMs in the cluster.  The possibilities are endless, but you will notice, having to say to management that “I blew it” was not one of the options.

Does this take the place of “Storage Class Memory” (SCM) aka persistent memory?  Not at all.  In fact, POWER10 has explicit support for SCM DIMMs.  The question is more of whether SCM technology is ready for HANA.  At 3 to 5 times worse latency than DRAM, Intel’s SCM, Optane, most certainly is not.  In fact, I call it highly irresponsible to promote a technology with barely a mention of the likely performance drawbacks as has been done by Intel and their merry band of misinformation brethren, e.g. HPE, Cisco, Dell, etc.

I prefer IBM’s more measured approach of supporting technology options, encouraging openness and ecosystem innovation, and focusing on delivering real value with solutions that make sense now as opposed to others’ approaches that can lead customers down a path where they will inevitably have to apologize later when things don’t work as promised.  I am also looking forward to 2021 to see what sort of POWER10 systems and related infrastructure options IBM will announce.

 

 

[i] https://www.tomshardware.com/news/intel-barlow-pass-dimm-3200mts-support-15w-tdp
[ii] https://www.crn.com/news/components-peripherals/ibm-power10-cpu-s-memory-inception-is-industry-s-holy-grail-
https://www.servethehome.com/ibm-power10-searching-for-the-holy-grail-of-compute/hot-chips-32-ibm-power10-memory-clustering-enterprise-scale-memory-sharing/
[iii] https://www.hpcwire.com/2020/08/17/ibm-debuts-power10-touts-new-memory-scheme-security-and-inferencing/

 

 

August 19, 2020 Posted by | Uncategorized | , , , , , , , , , , | Leave a comment

POWER10 – Opening the door for new features and radical TCO reduction to SAP HANA customers

As predicted, IBM continued its cycle of introducing a new POWER chip every four years (after a set of incremental or “plus” enhancements usually after 2 years).[i]  POWER10, revealed today at HotChips, has already been  described in copious detail by the major chip and technology publications.[ii]  I really want to talk about how I believe this new chip may affect SAP HANA workloads, but please bear with me over a paragraph or so to totally geek out over the technology.

POWER10, manufactured by Samsung using 7nm lithography, will feature up to 15 cores/chip, up from the current POWER9 maximum of 12 cores (although most systems have been shipping with chips with 11 cores or fewer enabled).  IBM found, as did Intel, that manufacturing increasingly smaller lithography with maximum GHz and maximum core count chips was extremely difficult. This resulted in an expensive process with inevitable microscopic defects in a core or two, so they have intentionally designed a 16-core chip that will never ship with 15 cores enabled. This means that they can handle a reasonable number of manufacturing defects without a substantial impact to chip quality, simply be turning off which ever core does not pass their very stringent quality tests.  This will take the maximum the number of cores in all systems up proportionately based on the number of sockets in each system.  If that was the only improvement, it would be nice, but not earth shattering as every other chip vendor also usually introduces more or faster cores with each iteration.

Of course, POWER10 will have much more than that.  Relative to POWER9, each core will feature 1.5 times the amount of L1 cache, 4x the L2 cache, 4x the TLB and 2x general and 4x matrix SIMD.  (Sorry, not going to explain each as I am already getting a lot more geeky than my audience typically prefers.). Each chip will feature over 4 times the memory bandwidth and 4x the interconnect bandwidth.  Of course, if IBM only focused on CPU performance and interconnect and memory bandwidths, then the bottleneck would naturally just be pushed to the next logical points, i.e. memory and I/O.   So, per a long-standing philosophy at IBM, they didn’t ignore these areas and instead built in support for both existing PCIe Gen 4 and emerging PCIe Gen 5 and both existing DDR4 and emerging DDR5 memory DIMMS, not to mention native support for future GDDR DIMMs.  And if this was not enough, POWER10 includes all sorts of core microarchitecture improvements which I will most definitely not get into here as most of my friends in the SAP world are probably already shaking their heads trying to understand the implications of the above improvements.

You might think with all of these enhancements, this chip would run so hot that you could heat an Olympic swimming pool with just one system, but due to a variety of process improvements, this chip actually runs at 3x the power efficiency of POWER9.

Current in-memory workloads, like SAP HANA, rarely face a performance issue due to computational performance.  It is reasonable to ask the question whether this is because these workloads are designed with an understanding of the current limitations of systems and avoid doing more computationally intense actions to avoid delivering unsatisfying performance to users who are increasingly impatient with any delays.  HANA has kind of set the standard for rapid response so delivering anything else would be seen as a failure.  Is HANA holding back on new, but very costly (in computational terms) features that could be unleashed once a sufficiently fast CPU becomes available?  If so, then POWER10 could be the catalyst for unleashing some incredible new HANA capabilities, if SAP takes advantage of this opportunity.

A related issue is that perhaps existing cores can deliver better performance, but memory has not been able to keep pace.  Remember, 128GB DRAM DIMMS are still the accepted maximum size by SAP for HANA even though 256GB DIMMS have been on the market for some time now.  As SAP has long used internal benchmarks to determine ratios of memory to CPU, could POWER10 enable to the use of much more dense memory to drive down the number of sockets required to support HANA workloads thereby decreasing TCO or enabling more server consolidation?  Remember, Power Systems all featured imbedded, hardware/hypervisor based virtualization, so adding workloads to a system is just a matter of harnessing any unused extra capacity.

IBM has not released any performance projections for HANA running on POWER10 but has provided some unrelated number crunching and AI projections.  Based on those plus the raw and incredibly impressive improvements in both the microarchitecture and number of cores, dramatic cache and TLB increases and gigantic memory and interconnect bandwidth expansions, I predict that each socket will support 2 to 3 times the size of HANA workloads that are possible today (assuming sufficient memory is installed).

In the short term, I expect that customers will be able to utilize TDI 5 relaxed sizing rules to use much larger DIMMs and amounts of memory per POWER10 system to accomplish two goals.  For customers with relatively small HANA systems, they will be able to cut in half the number of sockets required compared to existing HANA systems.  For customers that currently have large numbers of systems, they will be able to consolidate those into many fewer POWER10 sytems.  Either way, customers will see dramatic reductions in TCO using POWER10.

As to those customers that often run out of memory before they run out of CPU, stay tuned for part 2 of this blog post as we discuss perhaps the most exciting new innovation with POWER10, Memory Clustering.

 

[i] https://twitter.com/IBMPowerSystems/status/1295382644402917376
https://www.linkedin.com/posts/ibm-systems_power10-activity-6701148328098369536-jU9l
https://twitter.com/IBMNews/status/1295361283307581442
[ii] Forbes – https://www.forbes.com/sites/moorinsights/2020/08/17/ibm-discloses-new-power10-processer-at-hot-chips-conference/#12e7a5814b31
VentureBeat – https://venturebeat.com/2020/08/16/ibm-unveils-power10-processor-for-big-data-analytics-and-ai-workloads/
Reuters – https://www.reuters.com/article/us-ibm-samsung-elec/ibm-rolls-out-newest-processor-chip-taps-samsung-for-manufacturing-idUSKCN25D09L
IT Jungle – https://www.itjungle.com/2020/08/17/power-to-the-tenth-power/

 

August 17, 2020 Posted by | Uncategorized | , , , , , , , , | Leave a comment

SAP Extends support for Business Suite 7 to 2027 and beyond … but the devil is always in the detail

The SAP world has been all abuzz since SAP’s announcement on February 4, 2020 about their extension of support for Business Suite 7 (BS7) which many people know as ECC 6.0 and/or related components.  According to the press release[i], customers with existing maintenance contracts will be able to continue using and getting support for BS7 through the end of 2027 and will be able to purchase extended maintenance support through the end of 2030 for an additional 2 points over their current contracts.

It is clear that SAP blinked first although, in an interview[ii], SAP positions this as a “proactive step”, not as a reaction to customer pushback.   Many tweets and articles have already come out talking about how customers now have breathing room and have clarity on support for BS7.  And if I just jumped on the bandwagon here, those of you who have been reading my blog for years would be sorely disappointed.

And now for the rest of the story

Most of you are aware that BS7 is the application suite which can use one of several 3rd party database options.  Historically, the most popular database platform for medium to large customers was Oracle DB, followed by IBM Db2.  BS7 can also run on HANA and in that context is considered Suite on HANA (SoH).

What was not mentioned in this latest announcement is the support for the underlying databases.  For this, one must access the respective SAP Notes for Oracle[iii] and Db2[iv].

This may come as a surprise to some, but if you are running Oracle 12.2.0.1, you only have until November of this year to move to Oracle 19c (or Oracle 18c, but that would seem pretty pointless as its support ends in June of 2021.)  But it gets much more fun as that is only supported under normal maintenance until March, 2023 and under extended support until March, 2026.  In theory, there might be another version or dot release supported beyond this time, but that is not detailed in any SAP Note.   In the best-case scenario, Oracle 12 customers will have to upgrade to 19c and then later to an, as yet unannounced, later version which may be more transition than many customers are willing to accept.

Likewise, for Db2 customers, 10.5, 11.1 and 11.5 are all supported through December, 2025.  The good news is that no upgrades are required through the end of 2025.

For both, however, what happens if later versions of either DB are not announced as being supported by SAP. Presumably, this means that a heterogeneous migration to Suite on HANA would be required.  In other words, unless SAP provides clarity on the DB support picture, customers using either Oracle DB or IBM Db2 may be faced with an expensive, time consuming and disruptive upgrade to SoH near the end of 2025.  Most customers have expressed that they are unwilling to do back to back migrations, so if they are required to migrate to SoH in 2025 and then migrate to S/4HANA in 2027, that is simply too close for comfort.

Lacking any further clarification from SAP, it still seems as if it would be best to complete your conversion to S/4HANA by the end of 2025.  Alternately, you may want to ask SAP for a commitment to support your current and/or planned DB for BS7 through the end of 2027, see how they respond and how much they will charge.

[i] https://news.sap.com/2020/02/sap-s4hana-maintenance-2040-clarity-choice-sap-business-suite-7/
[ii] https://news.sap.com/2020/02/interview-extending-maintenance-for-sap-s4hana/
[iii] https://launchpad.support.sap.com/#/notes/1174136
[iv] https://launchpad.support.sap.com/#/notes/1168456

February 6, 2020 Posted by | Uncategorized | , , , , , , , , | Leave a comment

Does Intel’s Optane DC Persistent Memory decrease TCO for SAP?

When this new type of persistent memory DIMM (PMEM) was announced by Intel about a year ago, improving restart times was the most important factor cited by Intel and vendors of systems that utilize Intel Cascade Lake processors.  Some of my previous blog posts have discussed the performance issues of PMEM and despite numerous searches, I can find no data presented by Intel or any other vendor to suggest that any improvement has occurred since this technology was made generally available.  Over time, and perhaps as more customers realized that faster restarts at the cost of slower operational performance might not be very compelling, the message started to morph into saving money.

Regarding TCO specifically for SAP Suite on HANA (SoH) and S/4HANA, let’s start with the basic assertion, i.e. PMEM is less expensive than DRAM.  This is documented by pricing which shows a 128GB PMEM DIMM costs approximately 60% of the cost of a 128 DRAM DIMM[i] on one site and 40%[ii]  on another site.  This discrepancy may result when one vendor shows effective prices and another list prices with the list price example showing a higher cost savings with PMEM.

I was interested to see what would happen with actual SAP instances.  For comparison, let us start with a conventional DRAM memory system and assume that after using appropriate sizing tools, we have determined that an SoH or S/4HANA system requires a total of 6TB of memory to support 3TB of data with 3TB dedicated to system and HANA working memory.  I chose 6TB because this fits perfects on most Intel systems using 4 processors and 48@128GB memory DIMMs.  This config also has the added bonus of no waste at all and maximized performance since parallelism is optimized when every memory channel is used.

By comparison, we need to figure out how much memory is required if we utilize PMEM.  The SAP note on persistent memory[iii] describes ratios of DRAM to PMEM ranging from 2:1 to 1:4. For SoH and S/4HANA, the advice given is to run QuickSizer, /SDF/HDB_SIZING or ZNEWHDB_SIZE depending on where you are starting from.  I asked 3 different customers, one small, one medium and one very large, to provide me with the output of their sizing reports based on existing ECC systems.  I have included two key sections for the midsized customer:

Screen Shot 2020-02-04 at 11.57.33 AM

The Persistent Memory FAQ[iv] says: “Persistent memory can be used for the main storage of column store table that is typically the dominating factor of data space consumption in SAP HANA environments. Other areas like delta storage, caches, intermediate result sets or row store remain solely in dynamic RAM (DRAM). Disk LOBs (SAP Note 2220627) are also not part of the persistent memory.”  If you add up the numbers above using this rule, you may notice that this means that when using persistent memory, the amount of data housed in PMEM vs. DRAM does not fit with any of the ratios mentioned earlier.  Looking at the sizing reports that I obtained, the amount of PMEM vs. DRAM was more in the range of 1:1.5[v].

Now, let’s apply the very best ratio of the three reports, i.e. the very large customer, to our 6TB example above and we see that we need 6TB x .433 = 2.53TB PMEM and 6TB x .567 = 3.47TB DRAM.  Assuming 128GB DIMMs, this translates to 20.2 PMEM DIMMs and 27.8 DRAM DIMMs which rounded up comes to 21 and 28 DIMMs, i.e. 49 DIMMs total.  Clearly, this is one more than the max number (48) in a 4-socket system.  In addition, SAP note 2786237 states that a configuration must have: “Homogeneous symmetrical assembly of DRAM and PMEM DIMMs with maximum utilization of all memory channels per processor”, so the minimum configuration would be 28 of each type of DIMM for a total of 56 DIMM slots.

To the best of my knowledge, no Cascade Lake system supports this number of DIMM slots.  Several vendors support 64 DIMM slots on a 6 or 8-socket system.  Those that do not would require a 96 DIMM slots configuration.  At 64 DIMM slots, this configuration would waste the difference between the HANA memory requirement and the system configuration requirement, i.e. 540GB of DRAM and 1,508GB of PMEM would be wasted.  At 96 DIMM slots, the waste would be 2,588GB and 3,556GB respectively.  With either a 64 DIMM slot or 96 DIMM slot configuration, instead of a relatively affordable 4-socket system, a significantly more expensive 6 or 8-socket system would be required.

I chose to use the best pricing that I could find for DIMM prices assuming that other vendors would be able to match these prices.  I then applied that pricing to those vendors that can utilize  64 DIMM slots on a 6 or 8-socket configuration.  After a simple calculation[vi], the cost of just the memory of the DRAM+PMEM system came out $7,648 higher than the DRAM only system.  And remember, this is before adding in any additional costs for more processors and a system which can support more processors.

Of course, 256GB DRAM DIMMs could be used, reducing the DRAM DIMM count to 15, but this raises a thorny issue; No appliance has been certified by SAP[vii] with 256GB DRAM DIMMs.  Even if we ignored that issue and went out on a limb using TDI V5 relaxed rules, the significantly higher cost of 256GB DRAM DIMMs over 128GB DRAM DIMMs[viii] plus the need to round up to 24 DIMM slots would result in a configuration that was still substantially higher cost than the DRAM only configuration.

Any way that you cut it, the use of PMEM in a realistic SoH or S/4HANA configuration results in a higher cost of acquisition than a DRAM only configuration.  In other words, as shown in the previous blog posts, performance takes a major hit when using PMEM for HANA, it does not save any money and actually costs more and the only potential gain comes from faster restarts.

[i] https://www.dell.com/en-us/work/shop/cty/pdp/spd/poweredge-r940/pe_r940_12229_vi_vp?configurationid=0163c707-0003-46a0-808a-3b55c864ba70
[ii] https://dcsc.lenovo.com/#/configuration/cto/7X13CTO1WW?hardwareType=server
[iii] https://launchpad.support.sap.com/#/notes/2786237
[iv] https://launchpad.support.sap.com/#/notes/2700084
[v] actual range was 41.5% to 43.3% for PMEM versus 58.5% to 56.7% for DRAM based on the small to very large reports
[vi] 48 x $2,670 = 128,160 (DRAM only), 32 x $1,574 + 32 x $2,670 = $135,808 (DRAM + PMEM)
[vii] https://www.sap.com/dmc/exp/2014-09-02-hana-hardware/enEN/appliances.html#viewcount=100
[viii] https://dcsc.lenovo.com/#/configuration/cto/7X13CTO1WW?hardwareType=server

February 4, 2020 Posted by | Uncategorized | , , , , , , , , , , , | 2 Comments