{
  "slug": "scsi-read-capacity",
  "term": "SCSI READ CAPACITY",
  "aliases": [
    "READ CAPACITY(10)",
    "READ CAPACITY(16)"
  ],
  "definition": "SCSI READ CAPACITY reports a block device's logical addressing range and block length through a 10-byte or 16-byte command descriptor block.",
  "note": "For a complete zero-based range, the block count is last LBA + 1; multiplying by logical block length gives addressable bytes, not filesystem free space. READ CAPACITY(10) returning FFFFFFFFh requires the 16-byte form to resolve capacity. [readcap-tool]\n\nREAD CAPACITY(16) adds protection, provisioning and logical-to-physical block information. Reported logical block length counts user bytes, excluding protection information and on-medium ECC. [readcap-manual]\n\nOn zoned devices, RC_BASIS qualifies the returned address. Code 00b covers the initial contiguous zone range without sequential-write-required zones; 01b identifies the logical unit's final LBA. [readcap-manual]\n\nIn sg3_utils v1.48, sg_readcap --brief prints hexadecimal values and its first value is already a block count. Do not add one again: 0x3e8 0x200 represents 1,000 blocks of 512 bytes, or 512,000 bytes. [readcap-tool]",
  "status": "shipping",
  "advantages": [],
  "limitations": [],
  "related": [
    "scsi",
    "scsi-logical-unit",
    "command-descriptor-block",
    "logical-sector",
    "physical-sector",
    "scsi-lbprz",
    "scsi-get-lba-status"
  ],
  "supersedes": [],
  "supersededBy": [],
  "firstSeen": null,
  "lastSeen": null,
  "updated": "2026-10-24",
  "citations": [
    {
      "id": "readcap-tool",
      "title": "sg3_utils v1.48: sg_readcap(8), description, brief/long options and ZBC field",
      "url": "https://raw.githubusercontent.com/hreinecke/sg3_utils/v1.48/doc/sg_readcap.8",
      "accessed": "2026-10-24"
    },
    {
      "id": "readcap-manual",
      "title": "Seagate SCSI Commands Reference Manual, Rev. L (2020), sections 3.24-3.25 and Table 135",
      "url": "https://www.seagate.com/files/staticfiles/support/docs/manual/Interface%20manuals/100293068L.pdf",
      "accessed": "2026-10-24"
    }
  ],
  "provenance": [
    "Source review of Seagate Rev. L and sg3_utils v1.48; no device commands or hardware measurements. The arithmetic assumes a complete zero-based range, not obsolete partial-medium queries."
  ]
}