Windows 8 Introducing 'UEFI Firmware, GPT Partitioning, LBA' for Larger Disks Support

Microsoft has enbled large disks and large sectors in Windows 8, in a November 29 blog post Bryan Matthew, program manager on the Storage & File System team said "In Windows 8 we build on this work by focusing on scale and capacity.""Windows 8 is the first OS with full support for both types of […]

Windows 8Microsoft has enbled large disks and large sectors in Windows 8, in a November 29 blog post Bryan Matthew, program manager on the Storage & File System team said "In Windows 8 we build on this work by focusing on scale and capacity."

"Windows 8 is the first OS with full support for both types of AF disks - 512e and 4K Native. To make this happen, we identified which features and technology areas were most vulnerable to the potential issues described above, and reached out to the teams developing those features to provide guidance and help them test hardware for these scenarios," blogged Matthew.

The issues addressed include:

  • Introduce new and enhance existing API to better enable applications to query for the physical sector size of a disk
  • Enhancing large-sector awareness within the NTFS file system, including ensuring appropriate sector padding when performing extending writes (writing to the end of the file)
  • Incorporating large-sector awareness in the new VHDx file format used by Hyper-V to fully support both types of AF disks
  • Enhancing the Windows boot code to work correctly when booting from 4K native disks

Matthew notes "Beginning with Windows 8, multiple new capabilities within Windows will necessitate UEFI. The combination of UEFI firmware + GPT partitioning + LBA allows Windows to fully address very large capacity disks with ease."

Adding he said "Our partners are working hard to deliver Windows 8 based systems that use UEFI to help enable these innovative Windows 8 features and scenarios (e.g. Secure Boot, Encrypted Drive, and Fast Start-up). You can expect that when Windows 8 is released, new systems will support installing Windows 8 to, and booting from, a 3TB or bigger disk."

Here's a preview:

Windows 8 booted from a 3 TB SATA drive with a UEFI system

"Hard disk manufacturers agreed to use a sector size of 4KB, which they call "Advanced Format (AF)," and they introduced the first AF drive to the market in late 2009. Since then, hard disk manufacturers have rapidly transitioned their product lines to AF media, with the expectation that all future storage devices will use this format."

As illustrated below, a "4KB physical sector can be logically addressed with 512-byte logical sectors." "In order to write to a single logical sector, the disk cannot simply move the disk head over that section of the physical sector and start writing. Instead, it needs to read the entire 4KB physical sector into a cache, modify the 512-byte logical sector in the cache, and then write the entire 4KB physical sector back to the media (replacing the old block). This is called Read-Modify-Write," explains Matthew.

Disks with this emulation layer to support unaligned writes are called 4K with 512-byte emulation, or "512e" for short. Disks without this emulation layer are called "4K Native."

Windows 8:  4KB physical sector can be logically addressed with 512-byte logical sectors

NTFS in Windows 8 fully leverages capabilities delivered by our industry partners to efficiently support very large capacity disks.