EX200 Create and configure file systems Practice Question
A technician runs 'mkfs.xfs /dev/sdb1' and later mounts it. The file system is reported as having a block size of 1024 bytes. What is the most likely reason?
⚠ Common exam trap
Red Hat often tests the misconception that XFS always uses a 4096-byte block size, leading candidates to overlook the automatic block size reduction on small partitions.
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
✓
The partition size is less than 1GB, so mkfs.xfs automatically used a 1024-byte block size.
Mkfs.xfs automatically selects a 1024-byte block size when the underlying partition is smaller than 1 GB. This is a built-in heuristic in the XFS filesystem to optimize metadata overhead and space utilization on small volumes. The technician did not specify a block size, so the tool applied this default behavior based on partition size.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The administrator used the -b size=1024 option.
Why it's wrong here
The command shown invokes mkfs.xfs without any -b flag, so there is no evidence that the administrator explicitly passed -b size=1024. While mkfs.xfs accepts -b to override the default block size, the observed 1024-byte block size is exactly what the utility automatically selects for a small partition, and it would appear the same way even without an explicit option. In this scenario, the automatic selection is the simpler and correct explanation.
- ✗
The block size setting was ignored due to a kernel limitation.
Why it's wrong here
XFS has no kernel limitation that forces a 1024-byte block size. The kernel reads the block size from the superblock at mount time and honors whatever power-of-two value mkfs.xfs wrote, from 512 bytes up to 64 KiB. If the filesystem had been created with 4096-byte blocks, the kernel would mount it with that larger block size without modification. A kernel limitation would also affect every XFS filesystem, which is clearly not the case.
- ✗
The default block size for XFS is 1024 bytes.
Why it's wrong here
The statement that the default block size for XFS is 1024 bytes is incorrect as a general rule. mkfs.xfs normally selects 4096-byte blocks for most filesystems, and it only reduces the default to 1024 bytes when the filesystem is smaller than 1 GiB. This size-dependent behavior means the default is not a fixed 1024 bytes but rather a value that depends on the detected filesystem size.
- ✓
The partition size is less than 1GB, so mkfs.xfs automatically used a 1024-byte block size.
Why this is correct
When the partition on /dev/sdb1 is smaller than 1 GiB, mkfs.xfs automatically uses 1024-byte blocks instead of the usual 4096-byte blocks. This tuning improves space efficiency on small volumes by reducing the overhead associated with larger blocks, such as internal fragmentation and per-block metadata structures. The administrator did not need to specify any option; this is the default behavior for sub-1 GiB XFS filesystems.
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