CompTIA Linux+ (XK0-006)System ManagementHard
A storage administrator checks a two-disk RAID 1 array and sees the following output from 'mdadm --detail /dev/md0': 'State: clean, degraded' and one device listed as 'removed'. After replacing the failed physical disk and creating a new partition /dev/sdc1, which command correctly restores full redundancy to the array?
- Amdadm --add /dev/md0 /dev/sdc1
- Bmdadm --stop /dev/md0
- Cmdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/sdc1
- Dmkfs.ext4 /dev/sdc1
Show answer & explanationAnswer & explanation
Correct answer: A. mdadm --add /dev/md0 /dev/sdc1
'mdadm --add' adds a new spare/replacement device to an existing degraded array, triggering a resync so the array returns to a fully redundant, healthy state. Using --create would destroy the existing array metadata instead of repairing it.
Why the other options are wrong
- B. --stop deactivates the array entirely, which is not a repair step.
- C. --create would build a brand-new array and destroy existing data/metadata rather than repair it.
- D. Formatting the raw partition directly bypasses RAID membership and won't repair the array.
mdadm RAID Recovery
When a RAID array becomes degraded due to a failed disk, mdadm --add integrates a replacement device and triggers resynchronization to restore redundancy.
- mdadm --detail shows array state (clean, degraded, etc.)
- --add re-adds a replacement/spare disk to an existing array
- --create only be used for building a new array, not repairing one
Memory trick: --add = 'adopting' a new disk into the existing RAID family after a loss