XenServer - Attach an existing HDD based SR

First off, while the server is turned off, physically connect the HDD
containing the SR you need to attach and boot up. Check BIOS to ensure
drive is detected.

Run the following commands in the XenServer console:

1. pvscan
(the above gets the existing SR UUID to use in next command)

2. xe sr-introduce uuid=93937a2a-bf78-af99-bd75-b275e9211e4c type=ext
name-label="Local EXT3 SR 2" content-type=user

3.ls -l /dev/disk/by-id/
(the above lists the SCSI ID to use in next command)

4.xe pbd-create sr-uuid=93937a2a-bf78-af99-bd75-b275e9211e4c
device-config:device=/dev/disk/by-id/scsi-SATA_Hitachi_HDS7230_MN1221F30D6L7D
host-uuid=37448bb1-fb14-49e3-8637-5aaf51565289
(the above generates a PBD UUID to use in next command)

5. xe pbd-plug uuid=984a0186-6ec0-1e53-4ee2-cbf204109b91

After that the existing volumes should be listed in XenCenter. You will
need to attach them to the relevant VM in the correct order, etc.

Source:
http://support.citrix.com/article/CTX120962