Hardware Reference
In-Depth Information
NTFS cluster 0, and because cluster 0 is 4K (eight 512-byte sectors) long, it will occupy sectors
LBA 63 through 70. The problem with this is that on a 4K-sector drive, this means that NTFS cluster
0 will be part of physical sectors 7 and 8. Likewise, NTFS cluster 1 straddles physical sectors 8 and
9. This means that every time Windows writes to one cluster, the hard drive has to perform two read-
modify-write operations, which significantly reduces performance.
Figure 9.5
shows how the 4K
NTFS clusters, 512-byte logical (emulated) sectors, and 4K physical sectors line up if the drive is
partitioned under Windows XP and earlier.
Figure 9.5. Default 4K sector drive partition alignment on Windows XP and earlier versions.
Starting with Vista, Windows was designed with an awareness of 4K sector drives, solid-state drives
(SSDs), and RAID arrays, all of which deal with data in blocks of 4K or larger. To accommodate
alignment for all these types of storage devices, Windows Vista and later automatically creates
partitions on 2,048-sector (1MiB) boundaries, which are an even multiple of the larger sectors or
storage units used by virtually any storage device.
Figure 9.6
shows how the 4K NTFS clusters, 512-
byte logical (emulated) sectors, and 4K physical sectors would line up if the drive were partitioned
under these operating systems.
Figure 9.6. Default 4K sector drive partition alignment on Windows Vista and later.
As you can see, Windows Vista and later versions automatically start the first partition at sector LBA
2048, which results in a perfect alignment between the 4K NTFS clusters and the 4K physical
sectors. In this case, NTFS cluster 0 would perfectly align with physical sector 256, and so on. Each
time one cluster is written, the drive will do a normal write of the matching physical sector, instead
of a multiple sector read-modify-write operation as would be the case with a misaligned partition.
Operating systems have used 4K cluster-based file systems (such as NTFS) for many years now.
These OSs will naturally work with 4K sector drives, as long as the start of each partition is properly
aligned.
Table 9.7
shows which OSs automatically create partitions properly aligned for 4K sector
drives (including SSDs).
Table 9.7. Typical 4K-Byte Sector Format
