EX200 Create and configure file systems Practice Question
A system has two logical volumes in the same volume group: 'lv_prod' (100% used) and 'lv_backup' (20% used). The administrator wants to allocate 5 GiB from 'lv_backup' to 'lv_prod' without unmounting any filesystems. Is this possible and why?
⚠ Common exam trap
Many exam-takers confuse LVM's ability to resize logical volumes online (which is true for both growth and reduction at the LVM layer) with the filesystem's ability to shrink online, forgetting that ext4 requires unmounting for shrink operations.
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
✓
No, because ext4 filesystems cannot be shrunk online; they must be unmounted.
Ext4 filesystems do not support online shrinking; they must be unmounted before reducing the logical volume. Since the administrator wants to shrink lv_backup (which is only 20% used) to free 5 GiB, the ext4 filesystem on that LV must be unmounted first. Without unmounting, the lvreduce operation would fail, making the scenario impossible as described.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Yes, use lvreduce and lvextend while mounted; ext4 supports online shrinking.
Why it's wrong here
ext4 does not support online shrinking. While resize2fs can grow a mounted ext4 filesystem, the shrink operation requires the filesystem to be unmounted, so running lvreduce and lvextend while the LV is mounted and the ext4 filesystem is active risks severe corruption or a failed reduction.
- ✗
No, because LVM does not allow freeing extents from an LV while it is active.
Why it's wrong here
LVM does allow an LV to be reduced while it is active; the restriction is on the filesystem, not the volume manager. After shrinking the ext4 filesystem offline with resize2fs, lvreduce can free extents from the LV, but because ext4 must be unmounted first, the entire operation cannot be done online.
- ✓
No, because ext4 filesystems cannot be shrunk online; they must be unmounted.
Why this is correct
ext4 filesystems can only be shrunk while unmounted; the resize2fs tool does not support online shrink. Therefore, to free space from an ext4 LV, the filesystem must be unmounted, shrunk, and then the LV reduced, meaning the operation cannot occur while the volume is in use.
- ✗
Yes, use lvresize to move extents between LVs directly.
Why it's wrong here
lvresize is used to change the size of a single logical volume, not to move extents between volumes. To transfer space, you must first shrink the filesystem and LV on the source, then extend the destination LV, a process that cannot be performed online for ext4.
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