ZoL block device (zvol) exported iSCSI - LIO fails with Logical unit communication failure / read/write fail
Solution 1:
I finally discovered what was causing this. Apparently the quota was bypassed and the storage got full, I have no idea why and with what exactly. I added another zfs pool (moved the disk to a bigger chassis), removed the refreserved from the original one so I can snapshot it and zfs sent the snapshot to the new pool. After this I was able to repair the LVM and XFS metadatas and re-mounted the block device with the data.