FAQ: Support statement for 512e and 4K Native drives for VMware vSphere and vSAN

Products

VMware vSAN

Issue/Introduction

This article provides FAQs about support for 512e and 4K Native (4Kn) drives
for GA versions of VMware vSphere and VMware vSAN (formerly known as Virtual SAN). Note:

This article applies to Direct attached HDD drives.
This article does not apply to external storage arrays as long as LUNs presented to ESXi initiators use 512 logical sector size (READ_CAPACITY should report 512 logical block).
512e SSDs/NVMe drives are supported with all supported ESXi releases as long as the controller supporting these SSD/NVMe drives is listed on vSphere VCG. For vSAN environments the controller has to be listed on the vSphere VCG for vSAN.
Please check with your vendor if their listed controller supports SSD/NVMe drives.

See also:
VMware Co mpatibility Guide (VCG) for all ESXi Releases
VMware Compatibility Guide (VCG) specific for vSAN Environments

Environment

VMware vSAN 6.2.x
VMware vSAN 6.5.x
VMware vSAN 6.7.x
VMware vSAN 6.6.x
VMware vSAN 8.0.x
VMware vSAN 7.0.x

Cause

Resolution

What are 4K Native and 512e drives?
Industry standard disk drives have been using a native (physical) 512 bytes sector size.
However, due to the increasing demand for larger capacities, the storage industry introduced new advanced formats that use 4KB (4096 bytes) physical sectors.

The disk sector size is an important factor in the design of Operating System and Hypervisor (collectively called OS here) software such as device drivers and file systems, because it represents the atomic unit of I/O operations on a disk drive. Not all OS versions have been modified to utilize 4KB sectors in the disk drives. Thus, the firmware of these newer devices may expose a logical sector size, which is either 4KB Native (4Kn) or 512B Emulation (512e).

4Kn is the advanced format in which the physical sectors and logical sectors are both 4,096 bytes in size.

512e is the advanced format in which the physical sector size is 4,096 bytes, but the logical sector size emulates 512 bytes sector size. The purpose of 512e is for the new devices to be used with OSs that do not support 4Kn sectors yet. However, inherently, 512-byte emulation involves a read-modify-write process in the device firmware for every write operation that is not 4KB aligned.

For example, a workload that does I/O operations that are either not aligned at a 4KB offset in bytes from the start of the disk or that are not 4KB multiples in length, one gets an alignment penalty caused by a read-modify-write process taking place in the drive for every write operation. The penalty is more pronounced for smaller operations. For larger I/Os, the per-operation latency is dominated by transfer times. Because many 512e drives are slightly faster than their older 512n counterparts, the alignment penalty is typically cancelled out after a certain operation size (say 256KB and larger, sometimes less).

In other words, even with 512e sectors, it is still preferable for the applications and the OS to perform 4KB aligned I/O for predicable performance. This is a general problem and not particular to any specific OS.

Also, the read-modify-write penalty applies to both magnetic disks (HDD) and solid-state disks (SSD), but due to the much lower number of IOPS of magnetic disks, the performance impact is more pronounced in that case.

This table compares native 512-byte sectors to the new advanced formats:

Format	Logical Sector Size	Physical Sector Size
512n	512	512
512e	512	4,096
4Kn	4,096	4,096

Do current GA versions of vSphere and VSAN support 4K Native drives?Yes, starting vSphere 6.7/7.x and vSAN 6.7/7.x, we support 4K Native Hard Disk Drives.
vSphere & vSAN will continue to expose 512n VMDKs to Guest OS as part of this support.
VMFS 6 datastore is required for vSphere deployments and no RDM support is available with 4KN HDDs at this time. Which version of vSphere and vSAN support 512e drives?vSphere 6.5/6.7/7.x and vSAN 6.5/6.7/7.x and later support 512e drives as direct attached drives.
vSphere & vSAN will expose 512n to Guest OS.
VMFS 6.0 is required for 512e drive support starting with vSphere 6.5.
Prior to version 6.5, direct attached drives which expose 512e to vSphere and vSAN are not supported (see exception below)
due to potential performance issues when using these drives.
For more information, see the Impact/Risks section.

Exception: vSphere 6.0 and newer versions support Physical Mode RDMs mapped to direct attached 512e drives.

What if 512e drives are behind a compatible RAID controller and the RAID controller is exposing the 512n drives to vSphere?
vSphere supports this configuration as long as the RAID controller is exposing the 512e drives as 512n format drives to vSphere.
The RAID controller must also be listed in the vSphere VCG.
For vSAN environments the controller has to be listed on the vSphere VCG for vSAN.
Consult your RAID controller vendor to check your configuration and ensure it will not have a negative performance impact on the workloads you want to run.

See also:
VMware Compatibility Guide (VCG) for all ESXi Releases
VMware Compatibility Guide (VCG) specific for vSAN Environments

Additional Information

FAQ：VMware vSphere および vSAN の 512e および 4K ネイティブドライブのサポート表明
 Dúvidas mais frequentes: Declaração de suporte do VMware vSphere e do VSAN às unidades 512e e 4K Native
Preguntas frecuentes: Pauta de admisión para unidades 512e y 4K nativas para VMware vSphere y vSAN
常见问题解答：适用于 VMware vSphere 和 vSAN 的 512e 和 4K Native 驱动器的支持声明

Impact/Risks:

vSphere/vSAN 6.0 and earlier versions have not been designed to use 4Kn/512e direct attached disk drives.
512e drives are supported only in version 6.5, 6.7, 7.x and later.

vSAN is optimized for 4K aligned I/O operations since version 6.0, including the new vsanSparse snapshot format.
However, due to limitations in older builds of ESXi, full utilization of 4k alignment was not possible.

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