Dell Poweredge R630 Disk Formats 512e And 4Kn

2015-01-05

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A Dell Technical White Paper
512e and 4Kn Disk Formats
This paper provides the context for 512e and 4Kn disk format
migration, as well as pointing out the long-term benefits to
customers and potential pitfalls to avoid when moving from
512-byte to 4K sector formats.
Dell Engineering
December 2013
2 512e and 4Kn Disk Formats
THIS WHITE PAPER IS FOR INFORMATIONAL PURPOSES ONLY, AND MAY CONTAIN TYPOGRAPHICAL ERRORS AND
TECHNICAL INACCURACIES. THE CONTENT IS PROVIDED AS IS, WITHOUT EXPRESS OR IMPLIED WARRANTIES OF
ANY KIND.
© 2013 Dell Inc. All rights reserved. Reproduction of this material in any manner whatsoever without the express
written permission of Dell Inc. is strictly forbidden. For more information, contact Dell.
Dell, the DELL logo, and the DELL badge are trademarks of Dell Inc. Other trademarks and trade names may be used
in this document to refer to either the entities claiming the marks and names or their products. Dell disclaims any
proprietary interest in the marks and names of others.
3 512e and 4Kn Disk Formats
Contents
1 Overview ......................................................................................................................................................................................... 4
2 Background ..................................................................................................................................................................................... 5
3 The long-term benefit of 4K sectors ........................................................................................................................................ 6
4 Understanding the impacts of the 4K transition..................................................................................................................... 6
4.1 512-byte sector emulation ............................................................................................................................................... 6
4.2 Small or runt writes ............................................................................................................................................................ 8
4.3 Mixing drives ........................................................................................................................................................................ 9
5 Preparing for and managing the 4K transition ........................................................................................................................ 9
5.1 Managing 4K sectors in the Windows environment ................................................................................................... 9
5.2 Enterprise Windows support for 4K sector media ...................................................................................................... 9
5.3 Managing 4K sectors in the Linux environment ........................................................................................................ 10
5.4 VMware support ............................................................................................................................................................... 10
5.5 Dealing with unaligned conditions ................................................................................................................................ 11
5.6 512e/4Kn application support ........................................................................................................................................ 11
6 Drive labels ..................................................................................................................................................................................... 11
7 Conclusion ..................................................................................................................................................................................... 12
8 Additional resources .................................................................................................................................................................... 12
4 512e and 4Kn Disk Formats
1 Overview
A change is coming in the hard drive industry. As storage densities dramatically increase, one of the most
elemental aspects of hard drive designthe logical block format size known as a sectorhas remained
constant. The storage industry is quickly ramping up efforts to transition to a new type of format for
media, known as Advanced Format, which has a 4KB physical sector size. This change brings two new
types of media to the enterprise market:
4KB"native:"This"media"has"no"emulation"layer"and"directly"exposes"4KB"as"its"logical"and"physical"
sector"size."The"overall"issue"with"this"new"type"of"media"is"that"the"majority"of"current"and"legacy"
applications"and"operating"systems"do"not"query"for"and"align"I/Os"to"the"physical"sector"size,"
which"can"result"in"unexpected"failed"I/Os.
512-byte"emulation"(512e):"This"media"has"an"emulation"function"and"exposes"512"bytes"as"its"
logical"sector"size"(similar"to"a"regular"disk"today),"but"makes"its"physical"sector"size"information"
(4KB)"available."The"overall"issue"with"this"new"type"of"media"is"that"the"majority"of"applications"and"
operating"systems"do"not"understand"the"existence"of"the"physical"sector"size,"which"can"result"in"a"
number"of"issues.
Table 1 Format types
Format type
Bytes per sector value
Bytes per physical sector value
512n
512
512
512e
512
4,096
4Kn
4,096
4,096
Beginning in late 2009, accelerating in 2010, and hitting mainstream in 2011 for client-based HDDs, hard
drive companies began migrating away from the legacy sector size of 512 bytes to a larger, more efficient
sector size of 4,096 bytes, generally referred to as 4K sectors, and now referred to as Advanced Format by
IDEMA (The International Disk Drive Equipment and Materials Association). Enterprise HDDs are also
moving to this format, but are slower in adoption. The first Advanced Format enterprise HDD became
available in 2012, with a limited set in 2013 and a more general distribution in 2014.
This paper provides the context for this migration, as well as the long-term benefits and potential pitfalls to
avoid when moving from 512 bytes to 4K sectors.
5 512e and 4Kn Disk Formats
2 Background
The legacy sector format contains a Gap section, a Sync section, an Address Mark section, a Data section
and Error Correction Code (ECC) section as shown in Figure 1.
Figure 1 Legacy sector format
The sector layout is structured as follows:
Gap"section:"The"gap"separates"sectors.
Sync"section:"The"sync"mark"indicates"the"beginning"of"the"sector"and"provides"timing"alignment.
Address"Mark"section:"The"address"mark"contains"data"to"identify"the"sector’s"number"and"location."
It"also"provides"status"about"the"sector"itself.
Data"section:"The"data"section"contains"all"of"the"users"data.
ECC"section:"The"ECC"section"contains"error"correction"codes"that"are"used"to"repair"and"recover"
data"that"might"be"damaged"during"the"reading"or"writing"process.
This low-level format has served the industry well for many years. However, as hard drive capacities have
increased, sector size has increasingly become a limiting design element in improving hard drive capacities
and error correction efficiency. For example, comparing the ratio of sector size to the total capacity of
earlier hard drives to more recent drives, the sector resolution has become extremely small. The resolution
of the sector (the ratio of sectors as a percentage of total storage) has become very fine and increasingly
inefficient as shown in Table 2.
Table 2 Sector resolution
Capacity
Total sectors
Sector resolution
40MB
80,000
.001%
400GB
800,000,000
.0000001%
Very fine resolution is good when managing small, discrete amounts of data. However, applications
common in modern computing systems manage data in large blocks, much larger in fact than the legacy
512-byte sector size. More importantly, the small 512-byte sector has consumed a smaller and smaller
amount of space on the hard drive surface as areal densities have increased.
The migration to larger sectors within the hard drive industry has become a fundamental need relative to
gaining improvements in error correction and achieving format efficiencies.
6 512e and 4Kn Disk Formats
3 The long-term benefit of 4K sectors
Since all hard drive manufacturers have agreed to transition to the Advanced Format sector, the industry
must adapt to and embrace this change to minimize potential negative side effects. Short-term benefits to
end users will not be dramatic in terms of immediate capacity increases. However, the migration to 4K-
sized sectors will most definitely provide quicker paths to higher areal densities and hard drive capacities,
as well as more robust error correction. Reducing the amount of space used for error correction code
improves format efficiency.
The legacy 512-byte sector has non-data-related overhead for the Gap, Sync and Address Mark sections
for every 512-byte. The new Advanced Format standard of a 4K-byte sector essentially combines eight
legacy 512-byte sectors into a single 4K-byte sector. The Advanced Format standard uses the same
number of bytes for Gap, Sync and Address Mark, but increases the ECC fields. This yields a format
efficiency of 97 percent, almost a 10 percent improvement. Together, the benefits of improved format
efficiency and more robust error correction make the transition to 4K sectors well worth the effort.
Properly managing this transition to capture the long-term benefits with minimal side effects is a key focus
for the hard drive industry.
4 Understanding the impacts of the 4K transition
As noted earlier, there are many aspects of modern computing systems that continue to assume that
sectors are always 512 bytes. To transition the entire industry over to the new 4K standard and expect all of
these legacy assumptions to suddenly change is simply not realistic. Over time, the implementation of
native 4K sectors, where both host and hard drive exchange data in 4K blocks, will take place. Until then,
Dell and our competition will also implement the 4K sector transition in conjunction with a technique
called 512-byte sector emulation.
The most critical aspect of a smooth and successful transition to 4K sectors used in Advanced Format is
performance. Whether you are a system builder, OEM, integrator, IT professional or end user building or
configuring a computer, to ensure you have the performance you need for a successful transition, use the
operating system to align partitions on a 4Kn drive boundary.
For operating system versions that are not 4K-sector aware, use third-party software or utilities to create
hard drive partitions. To ensure the software or utilities you are using are 4K-sector aware, check with your
Dell team.
4.1 512-byte sector emulation
The introduction of 4K-sized sectors depends heavily on 512-byte sector emulation. This term refers to
the process of translating from the 4K physical sectors used in Advanced Format to the legacy 512-byte
sectors expected by host computing systems.
The 512-byte emulation is acceptable in that it does not force complex changes in legacy computing
systems. However, it carries the potential for negative performance consequences, particularly when
writing data that does not neatly correspond to eight translated legacy sectors, as evident by the 512-byte
emulation writing process.
7 512e and 4Kn Disk Formats
4.1.1 Emulated read and write processes
To read data from a 4K sector formatted drive in 512 emulation mode, the process is very straightforward,
as shown in Figure 7.
Figure 2 Potential read sequence for 512-byte emulation
The process of reading the 4K block of data and reformatting to the specific 512-byte emulated sector
requested by the host computer is performed in the drive’s DRAM memory and does not measurably
impact performance.
A write process will be more complicated, particularly when data the host computer attempts to write is a
subset of a physical 4K sector. In these cases, the hard drive must first read the entire 4K sector containing
the targeted location of the host write request, merge the existing data with the new data, and then
rewrite the entire 4K sector as shown in Figure 3. The fundamental reason for this is that the drive cannot
write just a portion of the 4K sector, but can only write the entire sector at once.
Figure 3 Potential write sequence for 512-byte emulation
In this instance, the hard drive must perform extra mechanical steps in the form of reading a 4K sector,
modifying the contents and then writing the data. This process is called a read-modify-write (RMW) cycle,
which is undesirable because it has a negative impact on hard drive performance. Minimizing the
probability and frequency of read-modify-write instances is the most important aspect of making the
transition to 4K sectors smooth and painless.
The causes of read-modify-write reduced performance include:
Write"requests"that"are"misaligned"because"of"logical"to"physical"partition"misalignment
Write"requests"smaller"than"4K"in"size
Write"requests"that"are"not"multiple"of"4K"in"size
8 512e and 4Kn Disk Formats
4.1.2 Aligned versus unaligned hard drive partitions
Up to now we have not discussed how host systems and hard drives communicate the location of sectors
on the media. It’s time to introduce the Logical Block Address (LBA).
Each 512-byte sector is assigned a unique LBA, from zero (0) to the number required based on the size of
the disk. The host requests a specific block of data using the assigned LBA. When the host requests to
write data, an LBA address is returned at the end of the write request telling the host where the data is
located. This becomes important in the transition to 4K sectors since for every 4K sector there are eight
different possibilities for where the host LBA starts.
When LBA 0 is aligned to the first virtual 512-byte block in the 4K physical sector, the logical to physical
alignment condition for 512-byte emulation is termed Alignment 0. Another possible alignment is when
LBA 0 is aligned to the second virtual 512-byte block in the 4K physical sector. This situation is termed
Alignment 1 and is shown in comparison to the Alignment 0 condition in Figure 4. There are six additional
possibilities for unaligned partitions that can result in read-modify-write events similar to the Alignment 1
condition.
Figure 4 Alignment conditions
Alignment 0 conditions work very well with the new 4K sectors in the Advanced Format standard. This is
because a hard drive can easily map eight contiguous 512-byte sectors into a single 4K sector by storing
512-byte write requests in the hard drive’s cache until enough contiguous 512-byte blocks are received to
form a 4K sector. Since modern computing applications deal with chunks of data that are typically larger
than 4K, runts (transfers smaller than 4K) are extremely rare. However, the Alignment 1 situation is another
matter.
When hard drive partitions are created that result in an unaligned condition as shown in Figure 4, read-
modify-write cycles occur that can slow hard drive performance. See section 5.5 for information on
avoiding these cycles when implementing Advanced Format hard drives.
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 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 modifying these processes to
maximize performance for the 4K transition.
9 512e and 4Kn Disk Formats
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 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 single 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 3 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"storage"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 3 Windows support
Drive formats Reported logical
sector size
Reported physical
Windows version with support
512-byte Native, 512n
512 bytes
All Windows versions
Advanced Format, 512e,
AF, 512-byte Emulation
512 bytes
Windows Server 2012
Windows Server 2008 R2 with MS
KB 982018
Windows Server 2008 R2 SP1
Windows Server 2008 with MS KB
2553708
Advanced Format, AF, 4K
Native, 4Kn*
4096 bytes
Windows Server 2012 (4k data disks
are supported and as boot disks in
UEFI mode)
Note that Windows Server 2003 and Windows Server 2003 R2 do not support 512e or 4Kn media. While
the system may boot up and operate minimally, there may be functionality issues, data loss, or sub-
optimal performance. Dell does not recommend using 512e media with Windows Server 2003.
10 512e and 4Kn Disk Formats
There are a number of software utilities (such as Diskpart and Paragon) that are widely used by system
builders, OEMs, value-added resellers, and IT managers for aligning partitions when the operating system
doesn't offer or support partition alignment out of the box. Systems today typically consist of multiple hard
drive partitions. This means that each partition on the hard drive must be created with 4K-aware
partitioning software to make sure proper alignment and performance is ensured.
5.3 Managing 4K sectors in the Linux environment
The key strategies in managing the transition to 4K sectors in a Windows environment also apply to Linux.
Table 4 Linux support
Drive formats Reported logical
sector size
Reported physical
Linux version with support
512-byte Native, 512n
512 bytes
All Linux versions
Advanced Format, 512e,
AF, 512-byte Emulation
512 bytes
RHEL 6.1*
SLES 11 SP2**
Ubuntu 13.10
Ubuntu 12.04.4
Advanced Format, AF, 4K
Native, 4Kn
4096 bytes
RHEL 6.1*
SLES 11 SP2**
Ubuntu 13.10
Ubuntu 12.04.4
*Red Hat® Enterprise Linux® 6 supports 4K-sector devices as data disks. 4K-sector boot disks are supported in UEFI
mode only.
**SUSE® Linux® Enterprise fully supports 4KB/sector drives in all conditions and architectures with one exception. The
4KB/sector hard disk drives are not supported as a boot drive on x86_64 systems booting with a legacy BIOS.
Changes have been made to both the Linux kernel and utilities to support Advanced Format drives. These
changes ensure that all partitions on Advanced Format drives are properly aligned on 4K sector
boundaries. Kernel support for Advanced Format drives is available in kernel versions 2.6.31 and above.
Support for portioning and formatting Advanced Format drives is available in the following Linux utilities:
Fdisk:"GNU"Fdisk"is"a"command"line"utility"that"partitions"hard"drives."Versions"1.2.3"and"above"
support"Advanced"Format"drives.
Parted:"GNU"Parted"is"a"graphical"utility"for"partitioning"hard"drives."Versions"2.1"and"above"support"
Advanced"Format"drives.
5.4 VMware support
The key strategies in managing the transition to 4K sectors in a Windows environment also apply to
VMware. VMware is planning to release a 512e-aware operating system in late 2013 and a 4Kn-aware
operating system in 2015.
Table 5 VMware support
Operating system
512e
4Kn
VMware
ESXi 5.5 (Q4 2013)
Planned in 2015
11 512e and 4Kn Disk Formats
5.5 Dealing with unaligned conditions
Using a 4K-aware version of an operating system to create hard drive partitions is a simple, straightforward
method for avoiding unaligned conditions. Some third-party firms offer utilities that examine existing hard
drive partitions and realign them as needed. This alternative takes additional time and adds steps to the
system building or upgrading process. Ultimately, Dell will develop more sophisticated methods and
design systems to manage unaligned conditions to mitigate negative performance impacts.
5.6 512e/4Kn application support
Not all applications are 4K physical sector aware. Table 6 summarizes the 4K application support. When an
application is 512e/4Kn aware, the I/Os will be compliant to the file system partition, and the drives will run
at expected performance level.
Table 6 Application support
Application
512e
Comments
Oracle
Yes
Microsoft Exchange
Yes
4Kn support ~2014*
SQL
Yes
VDI
Yes
4Kn support ~2015**
*It is more of supportability issue that Microsoft has not fully tested/validated Exchange with 4Kn drives. Since
Exchange does its own replication, it is very sensitive to the disk types, in particular to disk sector sizes and does not
recommend having different disk types as part of the same Database availability group. There are issues where the
replication can fail; for example, you have a 512n disk hosting one DB copy and a 512e disk hosting another DB copy.
See the following article for more details: http://blogs.technet.com/b/exchange/archive/2013/04/24/exchange-2010-
database-availability-groups-and-disk-sector-sizes.aspx
**VMware may support 4Kn drives in 2014. VMware currently supports 512e formats.
6 Drive labels
The AF Logo Program was created by IDEMA and the Advanced Format Marketing Work Group to easily
identify hard disk drives that employ long sector, AF technologies. While usage of the logo is optional, AF
logos may be seen populating hard drive product labels, product pages, and various literatures to indicate
the usage of AF technologies versus legacy sector size architectures that were used in earlier drives.
The AF emulation logo has one rounded corner and is used on any client or enterprise hard drive that is
equipped with industry-standard emulation techniques. AF 512e is the current standard by which
downward compatibility with legacy sector formats is achieved.
The AF native logo identifies the presence of AF native technologies, where data using long data sector
format standards is both recorded on the drive and passed to the host in the AF format. Unlike AF
emulation, there is no modification of the sector size by which the data is processed or communicated to
the host.
12 512e and 4Kn Disk Formats
Figure 5 Advanced Format emulation logos
Figure 6 Advanced Format native logos
7 Conclusion
The industry transition away from the legacy 512-byte sector is a certainty, and gives hard drive suppliers
another tool for driving improved areal densities. Dell and our customers both benefit from this transition
through higher capacity hard drives and continued reliability.
The key to a smooth transition is a well-educated storage community who can avoid potential
performance pitfalls. The most critical aspect of a smooth and successful transition to 4K sectors used in
Advanced Format is performance. Whether you are building or configuring a computer, do the following
to ensure optimal performance:
Use"an"operating"system"to"align"partitions"on"a"4Kn"boundary
Use"third-party"software"or"utilities"to"create"hard"drive"partitions;"verify"with"your"Dell"team"to"
ensure"the"products"you're"using"have"been"updated"and"confirmed"to"be"4K
Together with our industry colleagues and customers, we can make the transition to Advanced Format 4K
sectors smooth and efficient, leveraging the long-term potential benefits for Dell and our customers.
8 Additional resources
http://www.seagate.com/tech-insights/advanced-format-4k-sector-hard-drives-master-ti/
http://msdn.microsoft.com/en-us/library/windows/desktop/hh848035(v=vs.85).aspx
http://blogs.technet.com/b/exchange/archive/2013/04/24/exchange-2010-database-availability-groups-
and-disk-sector-sizes.aspx
http://www.idema.org/?page_id=2900
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