This article describes how to add a USB Drive to Citrix XenServer as a Local Storage Repository.  This is tested on XenServer versions: 5.0, 5.5, 5.6.

1. Plug in USB drive
2. Open up the CLI console
3. Check disks that are currently available:
   # fdisk -l
   Disk /dev/sdb is my 512mb usb drive
4. Now to check what ID the harddrive has assigned. Change directory…
   # cd /dev/disk/by-id/
   …and list the disks:
   # ls
5. Add the disk to the system:
   # xe sr-create type=lvm content-type=user device-config:device=/dev/disk/by-id/ usb-USB_Flash_Drive_AA04012700007933 name-label=”Local USB Storage”

Now you can see it in XenCenter and use it.

Créditos: http://blogs.citrix.com/2010/10/18/how-to-add-a-usb-drive-to-citrix-xenserver-as-a-local-sr-storage-repository/