Understanding Persistent Memory allocation based on HDB_SIZING report

[cosmo83]

Dear SAP folks,

We are trying to move our existing HANA infrastructure based on S4HANA 1610, from one provider to another. We would like to ideally take advantage of the persistent memory available on the newer hardware in the market.

There is a lot of confusion, on selecting the proper PMEM ratio for the operations.

Iam just doing a further dig deep into memory sizing.

If you are looking at the report for PMEM

From the study i have done till now and from the report, it shows that the Column Store Data is a good fit for persistent memory, and from the report also, the value looks good. Now the confusion starts at the PMEM ratio.

As per the report (Since Workspace is nothing but Row + Store Data), at the best i can have is 1:1 ratio of DRAM to PMEM. If the idea is to have at the best 1:1 ratio, why is SAP saying 1:2 , 1:4 ratios are also available.

Regards

Phani

[clement_mugner]

Hi Phani,

The other ratios are available for scenarios that are not S/4HANA or BW4HANA. To reduce cost i would recommend rather checking the HANA NSE feature than the PMEM.

But also note that the sizing report is estimating the work space (sometimes called "temporary memory") with a very simplistic formula that says: Work Space = Size of Column Store + Row Store. As you are already using HANA, i suggest you improve the sizing report estimation by checking what is actual memory usage peak on your server and use this value (with a margin) to estimate your actual DRAM requirement.

Example: Your peak is at 3,9TB. CS is 1,9TB. So work space, RS and hybrid LOB cache peak actually at 2TB (not 2,8TB as estimated by the report). This exercise improves your PMEM requirement estimation.

Best regards,

Clément

[sumitjais]

Hi Phani,

Just trying to understand your confusion.

"As per the report (Since Workspace is nothing but Row + Store Data), at the best i can have is 1:1 ratio of DRAM to PMEM. If the idea is to have at the best 1:1 ratio, why is SAP saying 1:2 , 1:4 ratios are also available"

Could you please suggest the reference where SAP says the ratio for DRAM : PMEM?

The note 2700084 - FAQ: SAP HANA Persistent Memory clearly states - " The share of persistent memory and DRAM depends on the amount of column store main storage data that exists in the system."