some operations (e.g. garbage collection/restore/etc.) are very read
intensive on the chunks, and having atime=on and relatime=off (zfs default)
makes those write intensive operations too. Additionally, 'ext4' defaults to
relatime, so also change the default for api-created zpools.
Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>