SAP HANA does not use vPMEM DAX in memory database

This document (000020271) is provided subject to the disclaimer at the end of this document.

Environment

SUSE Linux Enterprise Server 15
SUSE Linux Enterprise Server for SAP 15
SUSE Linux Enterprise Server HPC

Systems using DAX in memory filesystems, such as Intel Optane memory.

Situation

The memory is attached and visible, but it is not used by HANA.

root@geeko:/root# df -BG | grep pmem
/dev/pmem0                       269G  268G        2G 100% /hana/pmem/pmem0
/dev/pmem1                       757G    2G      756G   1% /hana/pmem/pmem1
/dev/pmem2                       373G    1G      372G   1% /hana/pmem/pmem2
/dev/pmem3                       403G    1G      402G   1% /hana/pmem/pmem3
/dev/pmem4                       394G  386G        9G  98% /hana/pmem/pmem4
/dev/pmem5                       596G  592G        5G 100% /hana/pmem/pmem5
/dev/pmem6                       405G  398G        8G  99% /hana/pmem/pmem6

Resolution

Double check that the 'dax' mount option is used to mount the filesystem.

See if the output of:

mount

for the mountpoint contains 'dax' as an option. If it does not add it to the mount options in fstab and remount the filesystem.

Also make sure that the xfs filesystem does not have the reflink option enabled. This is enabled implicitly by default during filesystem creation. The default crc=1 global metadata option will imply reflink=1

This can be option can be disabled only during filesystem creation.

man mkfs.xfs

Cause

DAX in memory filesytems must be mounted with the 'dax' option to be used as such.

XFS filesystems must not have the reflink option enabled.

There are other reasons why HANA might not be able to use the in memory filesystem. These are the two most common ones.

Additional Information

Kernel documentation can be found here:

https://www.kernel.org/doc/Documentation/filesystems/dax.txt

man mkfs.xfs

Intel Optane documentation (external link)

IBM vPMEM documentation (external link)

Disclaimer

This Support Knowledgebase provides a valuable tool for SUSE customers and parties interested in our products and solutions to acquire information, ideas and learn from one another. Materials are provided for informational, personal or non-commercial use within your organization and are presented "AS IS" WITHOUT WARRANTY OF ANY KIND.

Document ID:000020271
Creation Date: 04-Jun-2021
Modified Date:02-Jul-2021
- SUSE Linux Enterprise Server
- SUSE Linux Enterprise Server for SAP Applications
- SUSE Linux Enterprise HPC

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