[arch-general] systemd + crypttab

Hi. I've a system where there's a harddisk encrypted with luks and a lvm pv over it, used for backup. This disk is never removed or inserted while system is online, but not in every boot up it's present. Setting this volume in crypttab, when disk is absent, cryptsetup service hangs for several seconds, before timing out and allowing systemd to complete boot. There's any way of avoiding this, may be putting it to background, or something like this? Thanks,