As hard drive technology advances, much of the noise in the storage space revolves around solid-state drives, but there is another change taking place as well -- the hard drive industry’s transition to a 4K sector model from the old 512-byte model.
Hard drives traditionally allocate 512 bytes per sector, with another 50 bytes for error correction. Consequently, many drives sold today have about 8% to 9% of their available storage space reserved for nothing but low-level error correction. As hard drive technology has grown more reliable, however, there’s a push to increase the sector size from 512 bytes to 4096 bytes. This means less space is needed to store error correction data and more room is available for user data on the disk. Drives that use these 4K sectors are known as Advanced Format drives.
Here’s where things get interesting -- there’s more than one kind of Advanced Format drive. They fall into two basic categories -- native and emulation (or “512e”) drives. The native drives use 4K sectors on the platter and on the PC interface. The emulation drives use 4K sectors on the platter, but mimic a 512-byte sector drive on the interface. Note that 4K sector drives with no 512e support will not work and are currently not supported in the Windows OS. In theory, a 512e drive can connect to a system running a current version of Windows, such as Windows 7 or Windows Server 2008 R2 and has minimal problems.
However, the actual practice is very different and consists of two main points. For one, admins should install a couple of hotfixes (at least in the near term) that allow current editions of Windows to use 512e drives. The most crucial update is one attached to KB982018, which modifies the Windows Extensible Storage Engine subsystem API to work properly with 512e drives. It also alters a couple of other low-level Windows behaviors, such as how NTFS pads out write operations to the end of a sector.
Another key thing to be aware of is how certain applications like Hyper-V, SQL Server and Exchange do not deal well with the new sector size. For instance, Hyper-V may suffer a performance degradation of around 30% when VHD files are placed on 512e discs. Although this limitation won’t last forever, admins provisioning a system for Hyper-V need to be conscious of the implications that come with 512e volumes.
These aren’t the only issues that come with Advanced Format drives, but they are some of the largest found with the new format. The problems point to a general lack of readiness on Microsoft’s part for 4K sector drives, even in their 512e incarnations. To that end, admins planning on building Windows Server systems that use 4K or 512e drives should either avoid them for the time being or make sure they are not being used for data.
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ABOUT THE AUTHOR
Serdar Yegulalp has been writing about personal computing and IT for more than 15 years for a variety of publications, including (among others) Windows Magazine, InformationWeek and the TechTarget family of sites.