Choosing Correct Block Size for VMs running on iscsi over zfs.

crashpb

New Member
Aug 30, 2023
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hey everyone,
So rn I'm running the storage backend for my proxmox ve (8.2.4) box via zfs over iscsi.

Trunas core box provides the iscsi backend.

I have two storage pools on my truenas box:

HDD_Pool:
4x 8TB WD Reds running raidz2 ( atime 12 and 128k record size)

Nvme_Pool:
6x TB Samsung 990 Pros running raidz2 ( atime 12 and 128k record size)

I have added both of my truenas pools to proxmox via Thegrandwazoo 's tool as a zfs over iscsi target.

looking around I see a lot of different takes on what should the zvol blocksize for the vms be.

what would be the recommended block size for my current setup?

my use case is a mix of linux and windows VMs, and some VMs would be running mssql.

if I were to use the default 4k blocksize (of thegrandwazoo 's plugin) will there be any major performance hit to any of my vms?

what I understand currently is that with record size of 128k I can have zvols with block size UPTO 128k however I'm still not sure if its a wise Idea to have zvols with different blocksize under the same dataset.