CompTIA A_ Certification All-In-One Exam Guide, Seventh Edition - Michael Meyers [180]
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NOTE Windows XP Home and Windows Media Center do not support dynamic disks, nor do any Vista editions besides Business and Ultimate.
Dynamic disks use an MBR and a partition table, but these older structures are there only for backward compatibility. All of the information about a dynamic disk is stored in a hidden partition that takes up the last 1 MB of the hard drive. Every partition in a partition table holds a 2-byte value that describes the partition. For example, an extended partition gets the number 05. Windows adds a new number, 42, to the first partition on a dynamic disk. When Windows 2000 or XP reads the partition table for a dynamic disk, it sees the number 42 and immediately jumps to the 1-MB hidden partition, ignoring the old-style partition table. By supporting an MBR and partition table, Windows also prevents other disk partitioning programs from messing with a dynamic disk. If you use a third-party partitioning program, it simply sees the entire hard drive as either an unformatted primary partition or a non-readable partition.
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NOTE A key thing to understand about dynamic drives is that the technology is proprietary. Microsoft has no intention of telling anyone exactly how dynamic disks work. Only fairly recent Microsoft operating systems (Windows 2000 and up) can read a drive configured as a dynamic disk.
You can use five volume types with dynamic disks: simple, spanned, striped, mirrored, and RAID 5. Most folks stick with simple volumes.
Simple volumes work much like primary partitions. If you have a hard drive and you want to make half of it C: and the other half D:, you create two volumes on a dynamic disk. That’s it: no choosing between primary and extended partitions. Remember that you were limited to four primary partitions when using basic disks. To make more than four volumes with a basic disk, you first had to create an extended partition and then make logical drives within the extended partition. Dynamic disks simplify the process by treating all partitions as volumes, so you can make as many as you need.
Spanned volumes use unallocated space on multiple drives to create a single volume. Spanned volumes are a bit risky: If any of the spanned drives fails, the entire volume is permanently lost.
Striped volumes are RAID 0 volumes. You may take any two unallocated spaces on two separate hard drives and stripe them. But again, if either drive fails, you lose all of your data.
Mirrored volumes are RAID 1 volumes. You may take any two unallocated spaces on two separate hard drives and mirror them. If one of the two mirrored drives fails, the other keeps running.
RAID 5 volumes, as the name implies, are for RAID 5 arrays. A RAID 5 volume requires three or more dynamic disks with equal-sized unallocated spaces.
Other Partitions
The partition types supported by Windows are not the only partition types you may encounter; other types exist. One of the most common is called the hidden partition. A hidden partition is really just a primary partition that is hidden from your operating system. Only special BIOS tools may access a hidden partition. Hidden partitions are used by some PC makers to hide a backup copy of an installed OS that you can use to restore your system if you accidentally trash it—by, for example, learning about partitions and using a partitioning program incorrectly.
A swap partition is another special type of partition, but swap partitions are only found on Linux and BSD systems. A swap partition’s only job is to act like RAM when your system needs more RAM than you have installed. Windows has a similar function called a page file that uses a special file instead of a partition. Most OS experts believe a swap partition is a little bit faster