vSphere 6.5 introduces a new VMFS 6 – but why we need new version You ask? –answer: to support new hdd type, and this point us to current storage market situation . Well because with 512bytes sector size HDD’s vendors are hitting drive capacity limits. They can not go beyond a certain size without compromising the resilience and reliability (not the best option in case of our data). To provide large capacity drives, Storage Industry is moving forward to Advance format (AF) drives. These drives use large physical sector size of 4096 bytes.
So how does it help? With new AF (4K sector size) format, Disk drive vendors can create more reliable and large capacity HDD to support the growing storage needs. These drives are more cost effective as they provide better $/GB ratio.
Two kinds of 4k drives:
- 512 Emulation (512e) mode – these are 4KN drives but expose logical sector size as 512 and have physical sector size as 4K. This mode is important as it continues to work with legacy OS and application and provide large capacity drives. Main disadwantage with these drives is that they will trigger a RMW for storage I/O smaller than 4K. This RMW happens in drive firmware and may have some performance impact in cases where large # of storage IO are smaller than 4K
- 4KN Drives – these drives expose logical sector size and physical sector size as 4K. This drives can not work with legacy OS and application. Whole of the stack from vm guest OS to ESXi to Storage has to be 4KN
Lets now look at a few advantages of 4k drives.
- 4K drives require less space for error correction codes than regular 512-byte sector drives . This result in greater data density on 4k drives which provides a better TCO(total cost of ownership) ,
- 4K drives have a larger ECC field for error correction codes and so inherently provide better data integrity,
- 4k drives are expected to have better performance than the current 512n drives. However this is only true when the guest OS has been configured to issue I/Os aligned to the 4K sector size.
New VMFS 6 SUMMARY:
- VMFS 5 does not support 4k drives even in emulation mode.If a 512e drives is formatted with VMFS-5 it is still recognized but this configuration is not supported by Vmware,
- VMFS-6 is designed from the ground up to support AF drives in 512e mode,
- VMFS-6 metadata is designed to be in alignment with the 4k sector size,
- 512e drives can only be used with VMFS-6.