Dell PowerEdge R630 - Manual (Page 2)

2 4K Sector HDD FAQ | Dell Inc., 2014
Terminology
Sector – An atomic unit of data transfer size from/to Hard Disk Drive
Logical Block Address (LBA) – An atomic unit of HDD sector address (location).
Physical Sector – Sector size at the HDD media level, normally is 512 bytes
Physical LBA – LBA layout on HDD media level, each LBA has the Physical Sector size
Logical Sector – Sector size defined at the host –to-disk drive interface. Normally the same size as
Physical Sector unless the HDD is emulating.
Logical LBA – LBA layout at host-to-disk drive interface, each LBA has the Logical Sector size.
1. What is a 4k sector HDD? How is it different from standard
512 bytes sector HDD?
4k sector HDD is a new generation HDD whose physical sector is 4k bytes. As HDD areal density
increases, the footprint of each physical sector shrinks. However, since the natural contamination
(dust, particulate, etc.) remains about the same size. The ratio between the footprint of the media
defect and the physical sector is increasingly larger. It requires more embedded ECC per each
physical sector to maintain the published sector error rate. By increasing the physical sector size to
4k bytes, the ratio is reduced therefore the ECC burden per physical sector is also reduced. The
larger physical sector not only improve format efficiency but also improve media defect correction
ability and S/N design margin. Current shipping HDDs are based on 512 byte physical sector and
logical sector.
2. What is 4k native HDD and what is 512 emulation (512e)
HDD?
There are two models of 4k sector HDD:
1. 4k native HDD is a 4k sector HDD whose logical sector is the same as physical sector. Therefore
the logical sector size is 4k bytes instead of the legacy 512 bytes. This is incompatible with legacy
BIOS and Operating System.
2. 512 emulation (512e) HDD is a 4k sector HDD whose logical sector is 512 bytes (not matching
with physical sector). It no longer has one-to-one relationship between physical sector and logical
sector. Instead, one 4k physical sector consists of eight logical 512 bytes sectors (4k bytes = 8 *
512 bytes). This is done to make the 512 emulation HDD compatible to legacy BIOS and Operating
System.