Hi Everyone...
I've already tried searching a bit on the forum and the Proxmox documentation.
I want to ask for some clarification about the "block size" (ashift) value suggested on the Proxmox Web Interface when adding or creating ZFS pools.
Lately, the UI has been suggesting a 16k block size, which would correspond to an
However, when I check the actual pool after creation:
Usually I'm finding the pool using
So it looks like the UI recommendation and the actual ZFS ashift value are not always aligned.
I’m wondering if this difference is intentional, and whether the suggested “block size” in the UI is meant as a hint or as an actual configuration parameter.
I also replicate the VM virtual disks from the NVMe pool to “shadow” copies on the HDD pool, so that if an NVMe drive fails I can spin up or restore those VMs quickly.
So in effect, I have two pools:
I’ve been using the default ashift=12 (4K) for both, assuming that would match most modern drives.
But since the UI now shows “16K,” I’m wondering:
I’d appreciate any clarification on what the Proxmox UI’s block size setting represents, and whether it’s something we should be matching manually to the pool’s ashift
I've already tried searching a bit on the forum and the Proxmox documentation.
I want to ask for some clarification about the "block size" (ashift) value suggested on the Proxmox Web Interface when adding or creating ZFS pools.
Lately, the UI has been suggesting a 16k block size, which would correspond to an
ashift=14
, (though I even remember for a while I was being suggested 8k instead).However, when I check the actual pool after creation:
Code:
zpool get all rpool |grep ashift
# I get:
rpool ashift 12 local
Usually I'm finding the pool using
ashift=12
which corresponds to a 4k alignment.So it looks like the UI recommendation and the actual ZFS ashift value are not always aligned.
I’m wondering if this difference is intentional, and whether the suggested “block size” in the UI is meant as a hint or as an actual configuration parameter.
My setup
I typically install Proxmox on a pair of large SATA drives (mirrored), and then use a separate NVMe drive (or mirror) for production VMs.I also replicate the VM virtual disks from the NVMe pool to “shadow” copies on the HDD pool, so that if an NVMe drive fails I can spin up or restore those VMs quickly.
So in effect, I have two pools:
- One for VM production (NVMe)
- One for backups / replicas (HDD mirror) in rpool
I’ve been using the default ashift=12 (4K) for both, assuming that would match most modern drives.
But since the UI now shows “16K,” I’m wondering:
- Is that 16K "block size" supposed to match the ashift value of the underlying pool?
- When there is a mismatch between the "block size" shown on the web interface and the actual ashift value of the pool, which one prevails? and what are the potential issues when they don't?
- What is the relationship between the “block size” shown in the web interface and the actual ZFS ashift value used by the pool?
- Should we be using an ashift value of 14 on the underlying NVME drives?
- Is this documented somewhere?
I’d appreciate any clarification on what the Proxmox UI’s block size setting represents, and whether it’s something we should be matching manually to the pool’s ashift