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11 512e and 4Kn Disk Formats
4.2 Small or runt writes
In modern computing applications, data such as documents, images and video streams are much larger
than 512 bytes. Therefore, hard drives can store these write requests in cache until there are enough
sequential 512-byte blocks to build a 4K sector. As long as hard drive partitions are aligned, the hard drive
can easily map 512-byte sectors into 4K sectors without any performance penalties. There are, however,
certain low-level processes, such as meta data writes for example, that can force a hard drive to handle
runt writes that are not associated with unaligned partitions. When I/O size is either smaller than 4K or not
a multiple of 4K-sector size, the drive must handle the RMW and small writes in the same way. Dell
recommends eliminating the sub-4K or non-4K multiple transfers to maximize performance.
4.3 Mixing drives
If you decide to use a mix of drive types, but do not resolve these issues, the overall storage performance
may be lower than expected. To mix drives, you must have a good understanding of the operating system,
applications, and the configuration such as RAID, volumes, and so on. To ensure compatible drive mix,
check with your Dell support team.
5 Preparing for and managing the 4K transition
Now that you understand the benefits of migrating to 4K sectors, as well as the potential impacts to
performance, let's look at ways to manage this transition through the context of applications and
operating systems.
5.1 Managing 4K sectors in the Windows environment
The most important aspect of managing the transition to 4K sectors is related to the 512-byte emulation
drive alignment issues described in section 4. Advanced Format drives work well in an Alignment 0
condition, where the physical-to-logical starting position are equal. Alignment conditions are created
when the hard drive partition(s) is created.
5.2 Enterprise Windows support for 4K sector media
Table 2 lists the Microsoft Windows support policy for various media and their resulting reported sector
sizes.
 Logical sector: The unit that is used for logical blocks addressing for the media. We can also think
of it as the smallest unit of write that the drive can accept.
 Physical sector: The unit for which read and write operations to the device are completed in a
single operation. This is the unit of atomic write.
Table 2 Windows support
Drive formats
Reported logical
sector size
Reported physical
sector size
Supported versions
512-byte Native, 512n
512 bytes
512 bytes
All Windows versions
1. Advanced Format, 512e,
AF, 512-byte Emulation
512 bytes
4096 bytes
Windows Server 2012
Windows Server 2008 R2 with MS
KB 982018
Windows Server 2008 R2 SP1