SAPonPower

An ongoing discussion about SAP infrastructure

Optane DC Persistent Memory – Proven, industrial strength or full of hype?

Intel® Optane™ DC persistent memory represents a groundbreaking technology innovation” says the press release from Intel.  They go on to say that it “represents an entirely new way of managing data for demanding workloads like the SAP HANA platform. It is non-volatile, meaning data does not need to be re-loaded from persistent storage to memory after a shutdown. Meanwhile, it runs at near-DRAM speeds, keeping up with the performance needs and expectations of complex SAP HANA environments, and their users.”  and “Total cost of ownership for memory for an SAP HANA environment can be reduced by replacing expensive DRAM modules with non-volatile persistent memory.”  In other words, they are saying that it performs well, lowers cost and improves restart speeds dramatically.  Let’s take a look at each of these potential benefits, starting with Performance, examine their veracity and evaluate other options to achieve these same goals.

I know that some readers appreciate the long and detailed posts that I typically write.  Others might find them overwhelming.  So, I am going to start with my conclusions and then provide the reasoning behind them in a separate posts.

Conclusions

Performance

Storage class memory is an emerging type of memory that has great potential but in its current form, Intel DC Persistent Memory, is currently unproven, could have a moderate performance impact to highly predictable, low complexity workloads; will likely have a much higher impact to more complex workloads and potentially a significant performance degradation to OLTP workloads that could make meeting performance SLAs impossible.

Some workloads, e.g. aged data in the form of extension nodes, data aging objects, HANA native storage extensions, data tiering or archives could be placed on this type of storage to improve speed of access.  On the other hand, if the SLAs for access to aged data do not require near in-memory speeds, then the additional cost of persistent memory over old, and very cheap, spinning disk may not be justified.

Highly predictable, simple, read-only query environments, such as canned reporting from a BW systems may derive some value from this class of memory however data load speeds will need to be carefully examined to ensure data ingestion throughput to encrypted persistent storage allow for daily updates within the allowed outage window.

Restart Speeds

Intel’s Storage Class memory is clearly orders of magnitude faster than external storage, whether SSD or other types of media.  Assuming this was the only issue that customers were facing, there were no performance or reliability implications and no other way to address restart times, then this might be a valuable technology.  As SAP has announced DRAM based HANA Fast Restart with HANA 2.0 SPS04 and most customers use HANA System Replication when they have high uptime requirements, the need for rapid restarts may be significantly diminished.  Also, this may be a solution to a problem of Intel’s own making as IBM Power Systems customers rarely share this concern, perhaps because IBM invested heavily in fast I/O processing in their processor chips.

TCO

On a GB to GB comparison, Optane is indeed less expensive than DRAM … assuming you are able to use all of it.  Several vendors’ and SAP’s guidance suggest you populate the same number of slots with NVDIMMs as are used for DRAM DIMMs.  SAP recommends only using NVDIMMs for columnar storage and historic memory/slot limitations are largely based on performance.  This means that some of this new storage may go unused which means the cost per used GB may not be as low as the cost per installed GB.

And if saving TCO is the goal, there are dozens of other ways in which TCO can be minimized, not just lowering the cost of DIMMs.  For customers that are really focused on reducing TCO, effective virtualization, different HA/DR methodologies, optimized storage and other associated IT cost optimization may have as much or more impact on TCO as may be possible with the use of storage class memory.  In addition, the cost of downtime should be included in any TCO analysis and since this type of memory is unproven in wide spread and/or large memory installations, plus the available memory protection is less than is available for DRAM based DIMMs, this potential cost to the enterprise may dwarf the savings from using this technology currently.

May 13, 2019 - Posted by | Uncategorized | , , , , , , , , , , , , ,

1 Comment »

  1. Alfred, very well summarized! Due to the fact that DCPMM can only replace DRAM in a fix ratio of 1:1, 1:2 or 1:4 and the fact that the amount of columnar store is less than 50% of the total amount of memory needed for SAP HANA this will lead to systems with too much memory installed in total than can be really flexibly used. So, in terms of TCO, flexibilty and performance the step ‚back’ with DCPMM can be harmful and costly in contrast to the expected positive effects….

    Comment by HANA on POWER (@HANAonPOWER) | May 13, 2019 | Reply


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