Hardware Reference
In-Depth Information
starts at LBA 63.
To check the alignment for the partition on the second drive, divide the starting offset of 1,048,576 by
4,096. The result is an even 256, which is an even number, indicating that this partition is properly
aligned. This in fact is equal to 2,048×512 bytes, indicating that the partition starts at LBA 2,048.
If you have misaligned partitions, you can use a third-party partitioning program like Parted Magic
(
www.partedmagic.com
)
to both create aligned partitions as well as move existing partitions into
alignment. In addition, most if not all the drive manufacturers that sell 4K sector drives (including
SSDs) offer partition alignment utilities that can create new aligned partitions or take existing
partitions and align them. Check with your drive manufacturer to see if such a utility is available. Of
course, you should back up any existing data on any drive before performing partition alignment or
creation.
Disk Formatting
There are two types of disk formats:
• Physical, or low-level formatting
• Logical, or high-level formatting
The
FORMAT
command on a hard disk performs only the high-level format. The low-level formatting
is done at the factory on all modern drives. In addition, partitioning is required before a volume can
be high-level formatted, because a hard disk is designed to be used with more than one OS or file
system and may have more than one partition or volume. Using multiple operating or file systems on
one hard drive is possible by partitioning, which creates multiple volumes on the drive. A
volume
or
logical drive
is any section of the disk to which the OS assigns a drive letter or name.
Consequently, preparing an HDD for data storage involves three steps:
1.
Low-level formatting (LLF; done at the factory)
2.
Partitioning
3.
High-level formatting (HLF)
Low-Level Formatting
During a low-level format, the tracks are divided into a specific number of sectors, creating the
intersector and intertrack gaps and recording the sector header and trailer information. The sector's
data areas are filled with a dummy byte value or a pattern of test values. For hard disks, the number
of sectors per track depends on the drive and the controller interface.
The original ST-506/412 MFM controllers always placed 17 sectors per track on a disk, ST-506/412
controllers with RLL encoding increased the number of sectors to 25 or 26 per track, and ESDI
drives had 32 or more sectors per track. The ATA drives found in PCs today can have anywhere from
17 to 2,500 or more physical sectors per track, and the number of sectors can vary among different
tracks.
Virtually all ATA drives use a technique called
zoned-bit recording
(ZBR), sometimes shortened to
zoned recording
, which writes a variable number of sectors per track. Without zoned recording, the
number of sectors (and therefore bits) on each track is a constant. This means the actual number of
bits per inch will vary. More bits per inch will exist on the inner tracks, and fewer will exist on the
outer. The data rate and rotational speed will remain constant, as will the number of bits per track.
Figure 9.7
shows a drive recorded with the same number of sectors per track.
