Chache writeback vs writeback (unsafe)

M

Maksimus

Member
May 16, 2022
78
3
13
Tell me which caching mode is better to use for maximum disk performance.
The server is installed on industrial nvme using zfs. The server does not use raid and there is no iron raid controller.
 
Unsafe can be faster because it lies about sync write commands being safely written (which they are not, yet) to disk. It really depends on your specific use case. Test for yourself to make sure the risk is worth it to you.
EDIT: If you have enterprise NVMe drives, then they probably already cache sync writes, which is safe because of the battery backup (PLP) and you'll see no performance increase.
 
Last edited:
Keep in mind that all caching modes besides none will use RAM to buffer data, which can increase your actual ram usage by a significant margin.
 
Maksimus said:
It will be memory usage additionally (plus to) arc cache zfs ?
Click to expand...
Jup, you cache twice or even three times in RAM:
1.) Inside VM
2.) on the virtualization layer
3.) ZFS ARC
Thats why it is usually recommended (and default) to use "none" as cache mode when using ZFS.
 
Last edited:
  • Like
Reactions: LnxBil
Dunuin said:
Jup, you cache twice or even three times in RAM:
1.) Inside VM
2.) on the virtualization layer
3.) ZFS ARC
Thats why it is usually recommended (and default) to use "none" as cache mode when using ZFS.
Click to expand...
Thanks for this succinct explanation. It makes sense that none is the default.

But, now I'm wondering why Writeback is the recommendation for Windows 11 guests at https://pve.proxmox.com/wiki/Windows_11_guest_best_practices .

Is Windows just that much a bear in VMs? :P
 
You must log in or register to reply here.
Top Bottom