scsi-write-same · shipping · also WRITE SAME (10), WRITE SAME (16), WRITE SAME (32)

SCSI WRITE SAME

SCSI WRITE SAME applies a repeated logical-block pattern to a contiguous LBA range and can request unmapping when supported.

Related Observatory article: SCSI WRITE SAME on hesela.com

The host normally supplies one block rather than the complete repeated payload; zero-fill is only one possible use. LBPWS and LBPWS10 advertise variant-specific UNMAP support. [1]

UNMAP=1 does not prove reclamation: The cited reference's Table 252 permits writing when deallocation or anchoring is not performed. For WRITE SAME(16), NDOB=1 omits data-out; LBPRZ=010b selects the provisioning initialization pattern, not necessarily zeros. Protection-information rules also apply. [2]

A zero block count may select the remaining device range; WSNZ can forbid it. This is a destructive operation, not a capability probe. [1]

NDOB controls data-out, not the block count. At the pinned implementation, omitting NUM leaves one block even with NDOB enabled. A manual example placed under whole-device zeroing omits NUM; its placement does not change that default. [3] [1]

Relations

related

SCSI UNMAP, SCSI LBPRZ, Logical block provisioning status, NVMe Write Zeroes, Data sanitization

Advantages

• Repeated-block initialization can avoid transferring the complete range from the host. [1]

Limitations

• Command variant, provisioning flags and device limits must be interpreted together. [1, 2]

Citations

1. sg3_utils sg_write_same manual, pinned author commit 1929463554c5: description, NDOB, NUM and UNMAP (accessed 2026-11-09)
2. Seagate SCSI Commands Reference Rev. M (June 2022), sections 3.77-3.79 and Table 252 (accessed 2026-11-09)
3. sg3_utils pinned source: DEF_WS_NUMBLOCKS, main option parsing and do_write_same encoding (accessed 2026-11-09)

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