LFCS Storage Management Practice Question
A system administrator needs to create a new ext4 filesystem on /dev/sdb1 with a reserved block percentage of 2% instead of the default 5%. Which command should be used?
⚠ Common exam trap
It's easy for candidates to confuse `-m` (reserved block percentage) with `-r` (revision number) or `-R` (RAID stride), or they incorrectly choose `tune2fs` which modifies an existing filesystem rather than creating a new one.
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
✓
mkfs.ext4 -m 2 /dev/sdb1
The `-m` flag in `mkfs.ext4` sets the reserved block percentage for the superuser, and specifying `-m 2` overrides the default of 5% to reserve only 2% of the blocks on the new ext4 filesystem on /dev/sdb1.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
mkfs.ext4 -m 2 /dev/sdb1
Why this is correct
The `-m` flag sets the reserved-blocks percentage, so `-m 2` allocates exactly 2% for root rather than the ext4 default of 5%, satisfying the stem's constraint. Running `mkfs.ext4` also creates the filesystem on the specified partition, `/dev/sdb1`, in a single command.
- ✗
mkfs.ext4 -R 2 /dev/sdb1
Why it's wrong here
mkfs.ext4's -R flag sets extended filesystem features, not the reserved block percentage, so it cannot apply the 2% value. The -m flag controls reserved blocks and would be correct here. The -R option is genuinely used for feature settings such as sparse_super or resize_inode.
- ✗
mkfs.ext4 -r 2 /dev/sdb1
Why it's wrong here
mkfs.ext4 has no -r option; reserved block percentage is set with -m, so this command errors out. It tempts because -r is a plausible shorthand for 'reserved', but the correct invocation is mkfs.ext4 -m 2 /dev/sdb1.
- ✗
tune2fs -m 2 /dev/sdb1
Why it's wrong here
tune2fs adjusts parameters on an existing filesystem; it cannot create the ext4 filesystem the scenario requires on /dev/sdb1. It tempts because -m 2 correctly sets the reserved percentage, which is the right tool when modifying an already-created filesystem rather than making a new one.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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