The following is a Linux Dictionary word of the day: ddrescue.
GNU ddrescue is a powerful Linux data‑recovery utility that copies data from one block device to another while intelligently handling read errors. Unlike the classic dd command, ddrescue:
- Skips bad sectors automatically
- Retries only the damaged areas
- Uses a log file to track progress
- Can resume recovery at any time
This makes it ideal for failing HDDs, SSDs, USB drives, SD cards, and corrupted partitions.
1. -d parameter
- Direct disk access mode
- Forces ddrescue to bypass the OS cache
- Reads directly from the hardware
Useful for failing drives where caching may cause delays or hangs
Use when: recovering from physically damaged or unstable disks.
2. -f parameter
- Force writing to a block device
- Required when the output target is a raw device (e.g., /dev/sdb)
- Prevents accidental overwrites by requiring explicit confirmation
- Use when: cloning disk → disk.
3. -r[n] parameter
Retry bad sectors
- -r tells ddrescue to retry failed reads
- -r3 retries 3 times
- -r0 means no retries
- -r-1 means retry forever
- Used when: you want to squeeze every last readable byte from a failing disk.
Here’s a clean, production‑ready ddrescue command:
ddrescue -d -f /dev/mdev /dev/mdev2 ddclone.log
Breakdown:
-d → direct disk access
-f → force writing to block device
/dev/mdev → source disk
/dev/mdev2 → destination disk
ddclone.log → log file tracking recovery progress
Why the log file matters
If the recovery is interrupted, you can resume instantly:
ddrescue -d -f /dev/mdev /dev/mdev2 ddclone.log
ddrescue reads the log and continues exactly where it left off.
Best Practices for Safe Data Recovery
- Always clone first, never work on the failing disk directly
- Use a separate physical disk as the destination
- Keep the log file on a healthy drive
- Avoid mounting the failing disk
- Use -r3 or -r5 for moderate retries
- For severely damaged drives, use -r-1 (infinite retries) cautiously
Compared to other tools, ddrescue stands out because it:
- Automatically handles bad sectors
- Optimizes read order for maximum recovery
- Uses a persistent log file
- Works on any block device
- Is fast, reliable, and open‑source
- For Linux admins, technicians, and digital forensics specialists, ddrescue is simply indispensable.
Key Takeaways
ddrescue is the safest and most efficient Linux tool for disk cloning and recovery
- Use -d for direct disk access
- Use -f when writing to block devices
- Use -r[n] to retry bad sectors
- Always create and preserve a log file
