Whilst move storage from local-lvm to TrueNAS ZFS over iSCSI: Warning: volblocksize (4096) is less than the default minimum block size (8192).


Dec 13, 2020
Hi! When I move a VM's storage from `local-lvm` to a TrueNAS Core based ZFS volume over iSCSI, I get the following warning:

Task viewer: VM 102 - Move disk

create full clone of drive scsi0 (local-lvm:vm-102-disk-0)
Warning: volblocksize (4096) is less than the default minimum block size (8192).
To reduce wasted space a volblocksize of 8192 is recommended.

In order to get ZFS over iSCSI working, I used the plugin https://github.com/TheGrandWazoo/freenas-proxmox

I have no idea how to approach this issue. As far as I know I have chosen every single default possible.

Please could someone give me some tips on what the next steps of the troubleshooting process is?
on the host with ZFS, what does zfs get volblocksize <name of ZFS> say? Please also share your storage configuration /etc/pve/storage.cfg.
ZFS host block size configuration for disk I'm moving:

zfs get volblocksize pool/vm-102-disk-0
NAME                PROPERTY      VALUE     SOURCE
pool/vm-102-disk-0  volblocksize  4K        -

PVE Storage configuration:

cat /etc/pve/storage.cfg
dir: local
    path /var/lib/vz
    content vztmpl,backup,iso

lvmthin: local-lvm
    thinpool data
    vgname pve
    content rootdir,images

lvm: new-lvm-volume
    vgname pve
    content images,rootdir
    shared 0

lvmthin: new-lvm-thin-volume
    thinpool data
    vgname pve
    content rootdir,images

zfs: iscsi3
    blocksize 4k
    iscsiprovider freenas
    pool pool
    target iqn.2005-10.org.freenas.ctl:target
    content images
    freenas_password secret
    freenas_use_ssl 0
    freenas_user root
    nowritecache 0
    sparse 1
zfs: iscsi3
    blocksize 4k
The setting is here. Because of this, new volumes allocated on the storage will get this volblocksize.


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