EX200 Configure local storage Practice Question
Exhibit
Personalities : [raid1] [raid0] [raid10]
md0 : active raid1 sdb1[1] sda1[0]
10485760 blocks super 1.2 [2/2] [UU]
unused devices: <none>Refer to the exhibit. The /proc/mdstat output shows a RAID1 array with two devices. One of the disks (/dev/sda1) fails. Which sequence of commands would be used to remove the failed disk and add a new replacement disk /dev/sdc1?
⚠ Common exam trap
Red Hat often tests the exact command syntax and flag order, and the trap here is that candidates confuse the valid flags (--fail vs --set-faulty) or assume --remove can be used directly without first marking the disk as failed.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
mdadm /dev/md0 --fail /dev/sda1; mdadm /dev/md0 --remove /dev/sda1; mdadm /dev/md0 --add /dev/sdc1
It uses the proper mdadm syntax with the device name immediately after the command, followed by the action and the disk. The --fail flag marks the disk as faulty, --remove removes it from the array, and --add adds the new replacement disk. This sequence ensures the array remains in a degraded state before safely replacing the failed component.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
mdadm --fail /dev/md0 /dev/sda1; mdadm --remove /dev/md0 /dev/sda1; mdadm --add /dev/md0 /dev/sdc1
Why it's wrong here
This command sequence places the action option before the array device. The correct mdadm syntax for component operations requires the array device to appear immediately after 'mdadm', followed by the operation flag and then the component device, e.g., 'mdadm /dev/md0 --fail /dev/sda1'. Because the option is in the wrong position, mdadm will fail to parse the arguments and will not perform the intended failure, removal, and addition.
- ✓
mdadm /dev/md0 --fail /dev/sda1; mdadm /dev/md0 --remove /dev/sda1; mdadm /dev/md0 --add /dev/sdc1
Why this is correct
This is the proper procedure to replace a failed disk in a RAID1 array. '--fail' marks the current disk as faulty, allowing the kernel to stop using it and flag the array as degraded. '--remove' then detaches the faulty device from the array, and '--add' enlists the replacement disk, triggering a rebuild that copies data from the remaining healthy mirror.
- ✗
mdadm /dev/md0 --set-faulty /dev/sda1; mdadm /dev/md0 --remove /dev/sda1; mdadm /dev/md0 --add /dev/sdc1
Why it's wrong here
The option '--set-faulty' is not a valid mdadm action; mdadm uses '--fail' to mark a component as faulty. If you try to run 'mdadm /dev/md0 --set-faulty /dev/sda1', mdadm will return an error and the disk will remain active. Consequently, the subsequent remove and add operations will not proceed as intended, so this entire sequence is invalid.
- ✗
mdadm /dev/md0 --remove /dev/sda1; mdadm /dev/md0 --add /dev/sdc1
Why it's wrong here
This sequence omits the required '--fail' step. In mdadm, a disk cannot be removed from an array while it is still considered active or in sync; the kernel will refuse the removal with EBUSY. Marking the disk as faulty first is mandatory to transition it to a 'faulty' state, after which removal and replacement can occur.
- ✗
mdadm /dev/md0 --replace /dev/sda1 --with /dev/sdc1
Why it's wrong here
The '--replace' and '--with' pair is not a recognized mdadm invocation. While some RAID tools offer a single replace command, mdadm's standard replacement workflow is instead a sequence of '--fail', '--remove', and '--add'. Using '--replace' will cause mdadm to exit with an unknown-option error, leaving the disk untouched and the array unchanged.
Quick reference
RAID Level Comparison
| RAID Level | Min Disks | Fault Tolerance | Read | Write | Usable Capacity |
|---|---|---|---|---|---|
| RAID 0 | 2 | None | Excellent | Excellent | 100% |
| RAID 1 | 2 | 1 disk | Good | Moderate | 50% |
| RAID 5 | 3 | 1 disk | Good | Moderate | 67–94% |
| RAID 6 | 4 | 2 disks | Good | Lower | 50–88% |
| RAID 10 | 4 | 1 disk per mirror | Excellent | Good | 50% |
RAID is not a backup strategy — it protects against disk failure but not against accidental deletion, ransomware, or site-level events.
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