Proxmox external Ceph Disk Cache remommendation

[sander93]

Hello,

I searched this forum and google but i cannot find the final aswer..

We have a Proxmox cluster with a remote Ceph Luminous cluster.

I see i get muge faster writes with Cache=writeback in the disk options in Proxmox, (random 4k up to 16x faster and Seq 10x faster) then with cache=none.

Now my questions
- is cache=writeback with Ceph save?

- and where will it be cache, proxmox host memory or ceph osd memory?

Thank you.

 

[Alwin]

- is cache=writeback with Ceph save?

As with any cache, if the node suddenly dies, so will the cache. By default Ceph's cache is 25 MiB.

- and where will it be cache, proxmox host memory or ceph osd memory?

Part of qemu, as it either is using librbd (user space) or krbd (kernel page cache).
https://pve.proxmox.com/wiki/Performance_Tweaks#Disk_Cache