Serverside merging of big files is "slow" - NC 16.x

Nextcloud version (eg, 12.0.2): 16.0.5
Operating system and version (eg, Ubuntu 17.04): Centos 7.6
Apache or nginx version (eg, Apache 2.4.25): 2.4.6
PHP version (eg, 7.1): 7.2

The issue we are facing:

We often sync/transfer larger files > 10 GB, up to 100 GB by sync client and/or by web interface.

The upload of the chunked file is fast as the wire allows, e.g. 1Gb (±100MB/s) or 10MB/s on an 100MBit DSL.

So syncing from Mac a 26 GB files is done in about 5 minutes. great!

But merging the chunks of that file goes with ± 5 MB/s

The server side store reads/writes ± 300MB/s …

Load (from top) and CPU usage are not that high.


What might impact the merging-performance of the chunks?

How could that may be speeded up?

Thanks & Regards . Götz