Map Physical Drives to Letters in UEFI Shell

This guide outlines how system administrators can inspect, assign, and manage logical drive mappings for physical storage devices within the Unified Extensible Firmware Interface (UEFI) Shell. By leveraging the built-in map command and hardware device paths, administrators can associate raw block devices or recognized file systems with persistent or custom drive designations (such as FS0:, FS1:, or user-defined aliases), enabling direct file operations and recovery tasks outside the operating system.

Understanding UEFI Drive Handle Types

The UEFI Shell classifies storage interfaces into two primary categories:

  • Block Devices (BLKx:): Represent raw, unformatted physical drives, disks, or individual partitions (e.g., BLK0:, BLK1:).
  • File Systems (FSx:): Represent partitions formatted with a file system natively recognized by UEFI (typically FAT16 or FAT32, and occasionally NTFS or EXT through vendor-specific drivers).

Step 1: List Current Mappings and Hardware Paths

Open the UEFI Shell and execute the map command to display all currently detected storage devices alongside their assigned logical handles and hardware device paths:

map -v

The -v (verbose) flag displays the complete UEFI Device Path for each device.

To identify which physical drive corresponds to a logical handle, inspect the device path string:

  • SATA Drives: Contain identifiers such as Ata(...) or Sata(...).
  • NVMe Drives: Contain identifiers such as NVMe(...).
  • USB Drives: Contain identifiers such as USB(...).

If a newly connected drive does not appear, refresh the device list by running:

map -r

Step 2: Assign a Custom Logical Drive Letter

To map a physical block device or an existing file system handle to a custom logical drive name, use the following syntax:

map <Name>: <TargetDevice>

For example, to map the first recognized file system (FS0:) to a logical drive named SYSTEM::

map SYSTEM: FS0:

To map a raw block device partition (for example, BLK2:) directly to a new file system handle called FS5::

map FS5: BLK2:

Once mapped, you can switch to the drive by typing its name followed by a colon:

SYSTEM:
ls

Step 3: Delete an Existing Mapping

If a logical letter needs to be reassigned or removed, use the -d flag:

map -d SYSTEM:

Step 4: Automate Mappings on Boot

Manual mappings created in an active UEFI Shell session are temporary and clear upon system reboot. To make custom drive mappings persistent:

  1. Navigate to the boot drive's root directory:

    FS0:

  2. Create or edit the startup.nsh script:

    edit startup.nsh

  3. Add your custom mapping commands to the file:

    map -r
map USBDATA: FS1:

  4. Press Ctrl + S to save and Ctrl + Q to exit the editor.

The UEFI Shell automatically executes startup.nsh upon launch, ensuring physical devices map to your preferred logical drive labels automatically.