The minimum physical storage unit of a hard disk drive (HDD) is a sector. The solid state drive (SSD) equivalent is a page. Storage device firmware abstract away their physical sectors into logical sectors that software can operate on. The size of this sector refers to the size of the smallest addressable unit on the disk.
- Physical sector size
- This is the smallest unit a physical storage device claims it can write atomically. For HDDs, it is the actual size of sectors in a platter. Traditionally, the physical sector size for HDDs was 512 bytes, meaning that each sector could hold 512 bytes of data. However, with the introduction of Advanced Format HDDs, the physical sector size was increased to 4096 bytes (4 KiB) for increased storage density and improved error correction capabilities. SSDs do not expose their actual NAND flash memory page size, which typically ranges from 4 KiB to 16 KiB, instead their reported physical sector size is the same as their logical sector size. For NVMe SSDs, if it is available, the Atomic Write Unit Power Fail (AWUPF) parameter value is used.
- Logical sector size
- The logical sector size, also known as the operating system sector size, represents the size of the sectors exposed to the operating system and applications. It is the sector size used for reading from and writing to the storage device at the software level. The logical sector size can differ from the physical sector size. For example, an Advanced Format HDD with a physical sector size of 4096 bytes may still present a logical sector size of 512 bytes for compatibility with older systems and applications.
The different "layers", namely the device, stacked block devices, and file systems, should utilize the same sector sizes. If they do not, the mapping process from the firmware's translation layer, although usually transparent, will result in overhead that can be avoided.
The current physical and logical sector sizes values can be listed with lsblk:
$ lsblk -td
NAME ALIGNMENT MIN-IO OPT-IO PHY-SEC LOG-SEC ROTA SCHED RQ-SIZE RA WSAME sda 0 4096 0 4096 4096 1 mq-deadline 64 128 0B nvme1n1 0 4096 0 4096 4096 0 none 1023 128 0B nvme0n1 0 4096 0 4096 4096 0 none 1023 128 0B
PHY-SEC shows the physical sector size and
LOG-SEC—the logical sector size.
Alternatively, the values for a specific drive can read from the following sysfs entries:
$ cat /sys/class/block/drive/queue/physical_block_size $ cat /sys/class/block/drive/queue/logical_block_size
Changing sector size
Some NVMe drives and "enterprise" SATA hard disk drives support changing their reported sector size using standard NVMe (
Format NVM from NVM Command Set Specification 1.0 or later) or ATA (
SET SECTOR CONFIGURATION EXT from ATA Command Set - 4 or later) commands, respectively. For hard disk drives this changes the logical sector size in order to match the physical sector size for optimal performance. While for NVMe solid state drives, both the logical and physical sector size values get changed.
SATA solid state drives typically do not support changing their sector size. Exception are certain Intel SATA SSDs that can change the reported physical sector size, but not the logical sector size. Follow #Intel to change their reported physical sector size.
Changing the sector size of a drive is a complex process that requires low-level formatting. As an alternative, you can manually specify the desired sector size when creating file systems on the drive to get optimal performance. See #dm-crypt and #File systems.
Advanced Format hard disk drives
To determine if the sector size of an Advanced Format hard disk drive can be changed, use the hdparm utility:
# hdparm -I /dev/sdX | grep 'Sector size:'
Advanced Format drives whose Sector Configuration Log lists multiple logical sector sizes will show a list of them:
Logical Sector size: 512 bytes [ Supported: 512 4096 ] Physical Sector size: 4096 bytes
Hard disk drives which do not support multiple changeable logical sector sizes will simply report the current sector sizes. E.g., an Advanced Format 512e drive:
Logical Sector size: 512 bytes Physical Sector size: 4096 bytes
An Advanced Format 4Kn drive:
Logical Sector size: 4096 bytes Physical Sector size: 4096 bytes
4Kn drives already have the optimal configuration out of the box and do not need special considerations when partitioning/formatting. They can be simply used as is.
If your SATA HDD supports multiple logical sector sizes and the optional ATA command
SET SECTOR CONFIGURATION EXT (e.g. Seagate drives advertising FastFormat support), you can use hdparm to change between the supported logical sector sizes. To set it to 4096 bytes, i.e. 4Kn, run:
# hdparm --set-sector-size 4096 --please-destroy-my-drive /dev/sdX
Afterwards, hdparm should report the logical sector size as 4096 bytes:
# hdparm -I /dev/sdX | grep 'Sector size:'
Logical Sector size: 4096 bytes [ Supported: 512 4096 ] Physical Sector size: 4096 bytes
NVMe solid state drives
Most solid state drives (SSDs) report their logical block address size as 512 bytes, even though they use larger blocks physically - typically 4 KiB, 8 KiB, or sometimes larger.
To check the formatted logical block address size (FLBAS) of an NVMe drive, use the Identify Namespace command:
# nvme id-ns -H /dev/nvme0n1 | grep "Relative Performance"
LBA Format 0 : Metadata Size: 0 bytes - Data Size: 512 bytes - Relative Performance: 0x2 Good (in use) LBA Format 1 : Metadata Size: 0 bytes - Data Size: 4096 bytes - Relative Performance: 0x1 Better
Metadata Sizeis the number of extra metadata bytes per logical block address (LBA). As this is not well supported under Linux, it is best to select a format with a value of 0 here.
Relative Performanceindicates which format will provide degraded, good, better or best performance.
smartctl can also display the supported logical block address sizes, but it does not provide user friendly descriptions. E.g.:
# smartctl -c /dev/nvme0n1
... Supported LBA Sizes (NSID 0x1) Id Fmt Data Metadt Rel_Perf 0 + 512 0 2 1 - 4096 0 1
To change the logical block address size, use
nvme format and specify the preferred value with the
# nvme format --lbaf=1 /dev/nvme0n1
You are about to format nvme0n1, namespace 0x1. WARNING: Format may irrevocably delete this device's data. You have 10 seconds to press Ctrl-C to cancel this operation. Use the force [--force] option to suppress this warning. Sending format operation ... Success formatting namespace:1
This should take just a few seconds to proceed.
Drives older than 2020 can block the
Format NVM command when used on systems that issue a non-standard "security freeze" at the end of POST. If
nvme format fails, try to suspend the system (make sure to use S3 sleep not S0ix) and then try running
nvme format again after waking it.
Using manufacturer specific programs
If the above generic utilities do not allow changing the sector size, it may still be possible to change it using an utility from the drive's manufacturer.
For Intel use the Intel Memory and Storage (MAS) Tool ( AUR) with the
-set PhysicalSectorSize=4096 option.
For Seagate useAUR.
Scan all drives to find the correct one, and print info from the one you found:
# openSeaChest_Basics --scan # openSeaChest_Basics -d /dev/sdX -i
Should print out information about the drive. Make sure to check the serial number.
Check the logical block sizes supported by the drive:
# openSeaChest_Format -d /dev/sdX --showSupportedFormats
If 4096 is listed, you can change the logical sector size to it as follows:
# openSeaChest_Format -d /dev/sdX --setSectorSize=4096 --confirm this-will-erase-data
This will take a couple of minutes, after which your drive now uses a 4K native sector size.
Aligning partitions correctly avoids excessive read-modify-write cycles. A typical practice for personal computers is to have each partition's start and size aligned to 1 MiB (1 048 576 bytes) marks. This covers all common page and block size scenarios, as it is divisible by all commonly used sizes—1 MiB, 512 KiB, 128 KiB, 4 KiB, and 512 B.
- fdisk, cfdisk and sfdisk handle alignment automatically.
- gdisk and cgdisk handle alignment automatically.
- sgdisk by default only aligns the start of partitions. Use the
--align-endoption to additionally enable partition size/end alignment.
- sgdisk by default only aligns the start of partitions. Use the
- Parted only aligns the start of the partition, but not the size/end. When creating partitions, make sure to specify the partition end in mebibytes or a larger IEC binary unit.
However, for this to work, the device needs to report the correct default sector size, see #Changing sector size.
cryptsetup luksFormat, you can check the sector size used by the LUKS2 volume with
# cryptsetup luksDump device | grep sector
If the default sector size is incorrect, you can force create a LUKS2 container with a 4K sector size and otherwise default options with:
# cryptsetup luksFormat --sector-size=4096 device
The command will abort on an error if the requested size does not match your device:
# cryptsetup luksFormat --sector-size 4096 device (...) Verify passphrase: Device size is not aligned to requested sector size.
If you encrypted your device with the wrong sector size, the device can be re-encrypted by running:
# cryptsetup reencrypt --sector-size=4096 device
mkfs.bcachefs,, , , and default to a 4096 byte sector size.
defaults to 1024 byte sectors for file systems smaller than 512 MiB and 4096 byte sectors for 512 MiB and larger.
defaults to 512 byte sectors, but will use 4096 for 512e and 4Kn disks.
, , and use the backing device's logical sector size. I.e. they will use 512 byte sectors for 512e disks and 4096 byte sectors for 4Kn disks.
ZFS) defaults to 512 (2⁹) byte sectors, the sector size should be set explicitly at pool creation if using advanced format disks with the parameter
-o ashift=12 (2¹², 4096 bytes).
If the storage device does not report the correct sector size, you can explicitly format the partitions according to the physical sector size.
In particular shingled magnetic recording (SMR) drives that are firmware-managed are severely and negatively impacted if using a logical sector size of 512 bytes if their physical sector size is of 4096 bytes. Those drives have different performance writing zones and remapping reallocation occurs while being idle, but during heavy active writes (e.g., RAID resilvering, backups, writing many small files, rsync, etc.), a different file system sector size could drop write speed to single digit megabytes/second, as the higher performance write areas get depleted, and the sector translation layer gets overworked on the shingled areas.
Here are some examples to set the 4096-byte sector size explicitly:
# mkfs.ext4 -b 4096 /dev/device
# mkfs.xfs -s size=4096 /dev/device
# mkfs.fat -S 4096 /dev/device
# mkfs.ntfs -Q -s 4096 /dev/device
# mkfs.udf -b 4096 /dev/device
# zpool create -o ashift=12 poolname raidz device0 … deviceN
- Western Digital’s Advanced Format: The 4K Sector Transition Begins
- White paper entitled "Advanced Format Technology."
- Failure to align one's HDD results in poor read/write performance. See  for specific examples.