EX200 Configure local storage Practice Question
A system has a logical volume that is thinly provisioned. The thin pool has a size of 100GB and the thin volume has a virtual size of 500GB. The administrator notices that the thin pool has only 5GB of data written so far. Which command will display the current data usage of the thin volume?
⚠ Common exam trap
It's easy for candidates to confuse filesystem-level usage (shown by `df`) with thin pool-level data usage, leading them to pick `df -h` which incorrectly reports the virtual size instead of the actual consumed space.
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
✓
lvs -o lv_name,data_percent
The `lvs -o lv_name,data_percent` command specifically displays the percentage of the thin pool that has been consumed by the thinly provisioned logical volume. For thin volumes, the `data_percent` field reports the actual data usage relative to the thin pool's capacity, which is exactly what the administrator needs to see the current 5GB usage against the 100GB pool.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
df -h /dev/mapper/vg01-thinvol
Why it's wrong here
The df utility reads the filesystem superblock to report used and available blocks for the mounted file system. For a thin volume, df shows only the percentage of the logical volume's capacity that is occupied by stored file data, not the consumption of the underlying thin pool's data blocks. Therefore, df can show the filesystem as 90% full while the thin pool is only slightly allocated, and it never provides the pool-level data_percent.
- ✗
lsblk /dev/mapper/vg01-thinvol
Why it's wrong here
lsblk enumerates block devices and their hierarchy by reading sysfs and udev, displaying attributes such as device name, size, type, and mountpoint. A thinly provisioned volume appears as a device with its virtual size, and the thin pool may appear as a separate device, but lsblk does not query LVM metadata or thin pool allocation statistics. It is purely a topology and geometry listing, so it cannot reveal how much of the thin pool's data area is being used.
- ✗
lvdisplay /dev/vg01/thinvol
Why it's wrong here
lvdisplay displays a human-readable summary of LVM logical volume configuration, including the logical volume's size, segment layout, and the thin pool that backs a thin volume. Although it confirms the association between the thin volume and its pool, the standard lvdisplay output does not include the pool's data_percent value; that dynamic allocation metric is available through the lvs reporting command. To retrieve the thin pool usage percentage, you must use lvs with fields such as data_percent or lvdisplay --maps.
- ✓
lvs -o lv_name,data_percent
Why this is correct
The lvs command with the -o lv_name,data_percent option is the direct LVM reporting mechanism for thin provisioning usage. It reads LVM metadata and displays, for each specified logical volume, its name and the percentage of the underlying thin pool's data area that the volume's stored data has consumed. This is the standard way to monitor how much of the shared thin pool each thin volume is actually using, and unlike df, it reflects device-mapper level allocation, not filesystem-level usage.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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