NVMe Block Size: 512 vs 4096 Bytes (Advanced Format)

Advanced Format is an industry term that refers to storage devices utilizing a physical sector size of 4096 bytes (4KiB), as opposed to the legacy 512-byte sectors. The motivation is to improve areal density, error correction efficiency, and overall storage reliability.

  • 512n (512 native): Both physical and logical sectors are 512 bytes (rarely used in modern devices).
  • 512e (512 emulation): The drive has a physical sector size of 4096 bytes but emulates 512-byte logical sectors for backward compatibility.
  • 4Kn (4096 native): Both physical and logical sectors are 4096 bytes.

NVMe LBA Formats

NVMe namespaces support multiple LBA formats (LBAF), as reported by the device. These can be queried using

nvme list
Node         Generic    SN Model  Namespace Usage            Format           FW Rev
--------------------------------- --------- ---------------- ---------------- --------
/dev/nvme0n1 /dev/ng0n1 99 XX     1         4.00 TB/4.00 TB  512   B +  0 B   L88888888

nvme id-ns -H /dev/nvme0n1 | grep '^LBA Format'
LBA Format 0: Metadata Size: 0 bytes - Data Size: 512 bytes - Relative Performance: 0x1 Better (in use)
LBA Format 1: Metadata Size: 0 bytes - Data Size: 4096 bytes - Relative Performance: 0 Best

Sometimes it’s not available:

nvme id-ns -H /dev/nvme7n1 | grep '^LBA Format'
LBA Format 0 : Metadata Size: 0 bytes - Data Size: 512 bytes - Relative Performance: 0 Best (in use)

ACHTUNG: Changing the LBA format typically requires a namespace reformat operation, which destroys all user data.

Technical Considerations and LVM Limitations

  • 4K sector (4096 bytes): Preferred for modern operating systems and applications. It reduces metadata overhead and increases efficiency in ECC and internal flash management (lower write amplification).
  • 512B sector (512 bytes): Maintained solely for backward compatibility with legacy systems and software that require 512-byte sectors.
  • When using LVM, ensure all physical volumes (PVs) are created on block devices with the same sector size. LVM migration (e.g., pvmove, lvconvert –merge, or extending a VG across multiple devices) will fail if the underlying block sizes differ (e.g., mixing 512B and 4K LBAs).

Implementation

Configure 4k format:

nvme format /dev/nvme0n1 --lbaf=1

Check:

nvme id-ns -H /dev/nvme0n1 | grep '^LBA Format'
LBA Format  0 : Metadata Size: 0   bytes - Data Size: 512 bytes - Relative Performance: 0x1 Better
LBA Format  1 : Metadata Size: 0   bytes - Data Size: 4096 bytes - Relative Performance: 0 Best (in use)

nvme list
Node         Generic    SN           Model          Namespace     Usage      Format           FW Rev
------------ ---------- ------------ -------------- --------- ---------------------- ----------------
/dev/nvme0n1 /dev/ng0n1 999999999999 CT4000T700SSD3     1     4.00TB/4.00TB  4 KiB +  0 B   P8888888

All done.

SpeedTest ( raw disk )

TBD ( fio )

SpeedTest ( ext4 )

TBD ( fio )