SAPonPower

An ongoing discussion about SAP infrastructure

SAP HANA support for HPE nPar on Superdome Flex update

In addition to the outstanding support for virtualization technologies like PowerVM for HANA and the lukewarm support for VMware by SAP, SAP also supports other technologies that allow larger systems to be subdivided into smaller nodes.  Note that I did not say virtualization, but subdivision.  Physical partitioning (PPAR) is a technology invented in the 1990s and only allows components, e.g. boards or NUMA nodes, to be allocated to a separate workload from others on the same physical system.

On October 22, 2018, SAP updated its SAP Note for HPE nPar technology.[i]  With this update, SAP now supports nPars with Superdome Flex.  Granularity is incredibly fine (not).  As noted in the SAP note, “Via nPartitions, the following  partition sizes are supported in terms of the number of sockets:

    • Skylake based architecture: ScaleUp 16s, 12s, 8s, 4s; ScaleOut 4s, 8s, 16s

Or to put it in terms of cores, each socket has 28 cores, so granularity is 112 cores.  You need only 20 cores?  No problem, you get to consume 112.  You need 113 cores? Also no problem, you get to consume 224 cores.  But, on the positive side, these npars are “electrically isolated” which has 2 really important implications.  First, the only way to isolate one or more Superdome Flex drawers into a separate nPar is to physically change the mesh wiring of the entire system.  That means that if you decide to change the configuration of nPars, dynamic changes would be the exact opposite of what is supported.  In fact, according to customer reports, HPE requires a Statement of Work service contract to come out and rewire the system and it takes multiple days … one customer reported multiple weeks.  The second implication is that all resources on the node(s) in an nPar are dedicated to that nPar.  In the above example, if you need 20 cores, you probably require around a ½ TB of memory for BW or 1TB of memory for S/4.  It is possible to configure an nPar with as little as 1.5TB of memory which means that you might waste an entire TB if you only need ½ TB.  Alternately, if you have other workloads on other nPars that require more cores and memory and you want to keep all drawers consistent to allow for future changes, you might actually have up to 6TB per drawer meaning much more wasted memory if you only require ½ TB for a particular workload.  By the way, the only other elements that are shared when a system is broken up into physically isolated nPars are the frame(s), power supplies and the RMC – Rack Management Controller.  PCIe cards cannot be shared due to the physical isolation, so by using nPars, you essentially take a very expensive system and carve it into a bunch of smaller and very expensive, isolated systems which are difficult to reconfigure.  Alternately, if you really must use HPE technology for smaller workloads, you could purchase smaller systems at much lower prices.

I have really been trying to scratch my head and understand why anyone would want this type of 1990s era partitioning technology.  HPE certainly does because it results in higher profits from selling larger systems with more aggregate capacity while giving the false appearance of flexibility.  For customers, on the other hand, it offers massive waste and very limited flexibility.

My advice: Don’t be a sucker and get taken in by HPE’s misdirection play.  Either purchase appropriately sized systems for each workload or purchase systems that offer real virtualization, such as IBM Power Systems, with fine grained allocation of resources sharing of components such as PCIe adapters and true server consolidation, but don’t purchase one of these massive HPE systems and then eliminate any perceived value of using such a large system by cutting it up into smaller systems.

 

 

[i]2103848 – SAP HANA on HPE nPartitions in production

 

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March 25, 2019 - Posted by | Uncategorized | , , , , , , , , , , ,

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