HP StorageWorks 2000 Series Reference Manual page 184

Rescan forces rediscovery of attached disk drives and enclosures. If both storage
controllers are online, it also forces re-evaluation of the enclosure IDs of attached
drive enclosures, so that IDs are assigned based on controller A's enclosure cabling
order. A manual rescan may be needed after system power-up to display enclosures
in the proper order.
A manual rescan is not required to detect when drives are inserted or removed; the
controllers do this automatically. When drives are inserted they are detected after a
short delay, which allows the drives to spin up.
When you perform a manual rescan, it temporarily pauses all I/O processes, then
resumes normal operation. It can take up to two minutes for the enclosure IDs to be
corrected.
To rescan, as an Advanced Manage user:
1. Verify that both controllers are up.
2. Select Manage > Utilities > Disk Drive Utilities > Rescan.
3. In the Rescan For Devices panel, click Rescan.