Dell PowerEdge R730xd - Manual (Page 4)

4 4K Sector HDD FAQ | Dell Inc., 2014
misaligned data, the 512e HDD must perform READ-MODIFY-WRITE functions to complete the
write operations. Therefore, 512e HDD suffers significant performance loss (50%) in the random
writes, misaligned data operations. In addition, a sudden power loss during READ-MODIFY-WRITE
operation could corrupt the physical sector causing data loss/corruption on adjacent logical
sectors within the affected physical sector. The host will not be aware of these corruptions on the
adjacent logical sectors since they were not part of the data transfer during the emergency power
loss condition.
4. What is Advanced Format?
Advanced Format is the term for 4k sector HDD or 512e HDD implementation.
5. What are the mitigations to 512e performance and data risk?
As stated before, the main reasons for 512e performance is mis-alignment during writes.
Newer operating systems and applications are 512e-disk aware and minimize the incident of
READ-MODIFY-WRITE. Writing data on an aligned 4K boundary and in multiple of 4k bytes
eliminates the READ-MODIFY-WRITE operation.
As of the date of this paper, most versions of Client, Cloud, and Cold drives do not have power-
loss-protection during READ-MODIFY-WRITE operation. An emergency power loss during READ-
MODIFY-WRITE operation of a physical sector (4k) could corrupt the adjacent logical sectors (512
bytes) within the affected physical sector.
Enterprise drives incorporate an advanced non-volatile cache system to buffer the READ-
MODIFY-WRITE operation.
There are three version of this non-volatile cache system:
1. Solid state non-volatile cache (NVC NOR flash or NVC NAND flash) using built-in spindle back-
EMF to power the flash.
2. Disk Media non- volatile cache aka. Media Based Cache (MBC or MC) using reserved area of
the drive media to buffer the non-aligned writes from the host
3. Combination of step 1 and step 2.
At the time of this paper, we are seeing various non-volatile cache implementations:
RMW Cache System Implemented in
None Client, Cloud, and Cold HDD
NVC solid state Vendor A&B for Nearline and Enterprise
drives
MBC/MC Vendor C for Nearline and Enterprise
drives
NVC + MC Available as proto for enterprise 512e
drives but no plan for production