I have a oracle linux 5.8 virtual server (virtualized via oracle virtual manager, which is using xen), which has a couple of luns attached via scsi. Now I wanted to attache more luns, but found that /sys/class/scsi_host/host0, which is the scsi host where the lun would be attached, is missing. It must have been there bevor, because I was able to attach the previous luns.
I have a feeling that rebooting the box would fix things, but since this is production, a reboot would cause some hassle.
Any ideas as to why this could be missing or how to get it back without a reboot?