alignment-offset · shipping · also alignment_offset, BLKALIGNOFF

Alignment offset

Alignment offset describes the byte displacement of a block device or partition start from the storage stack's natural alignment.

Query the path actually used. In Linux 6.12, bdev_alignment_offset incorporates a partition's start and returns -1 when the queue carries a misaligned-topology flag. This sentinel is not a byte displacement. [2]

The signed blockdev --getalignoff query preserves -1. Partition sysfs in that kernel instead formats the result as unsigned and can show 4294967295; do not apply either sentinel as an ordinary offset. [4] [3]

For compatible partition limits, Linux uses G = max(physical_block_size, minimum_io_size) and computes (G + parent_offset - (start_bytes mod G)) mod G. For G=4096, parent_offset=0 and start_bytes=1049088, the result is 3584, not 512. This is a calculated example, not a device observation. [2]

Relations

related

Partition alignment, Logical sector, Physical sector, Minimum I/O size, Optimal I/O size, Direct-I/O alignment

Advantages

• Distinguishes a partition's start geometry from its parent's queue-size hints. [1, 5]

Limitations

• A zero displacement does not establish correct buffer alignment for every I/O API. [1]

Citations

1. Linux 6.12: stable sysfs block ABI, sector sizes and I/O topology (accessed 2026-10-19)
2. Linux 6.12: block limits validation and bdev_alignment_offset (accessed 2026-10-19)
3. Linux 6.12: partition alignment_offset_show unsigned formatting (accessed 2026-10-19)
4. util-linux 2.40.2: signed BLKALIGNOFF query formatting (accessed 2026-10-19)
5. util-linux 2.40.2: lsblk explicit columns and inherited queue attributes (accessed 2026-10-19)

Further reading

6. Hesela: 512e, 4Kn and alignment: geometry is not durability (accessed 2026-10-19)

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