Disk Management — what is RAID, and how is it built?
The Logical Disk Manager and Administrator service is the service that manages disks on your computer. If this service is off, software disk management cannot be performed. Hardware RAID (via RAID cards) follows roughly the same logic. Disk management operations are performed via My Computer — Manage — Storage — Disk Management.

Disks are categorized in two types.
1. Basic Disc: Areas on a basic disk are called partitions. There are 2 partition types.
a. Primary Partition: the partition used to install the operating system. A hard disk can be divided into a maximum of 4 partitions. Also referred to as the primary memory partition.
b. Extended Partition: the disk is made extended and then a logical disk is created on it. These disks store only data; the OS cannot be installed on them.
In addition, if your external disk is dynamic, you have to start it every time you boot. The external disk should be made basic; otherwise issues may occur.
2. Dynamic Disc: dynamic disks use volumes instead of partitions. If you want to switch from dynamic to basic, all volumes must be deleted. The reverse does not require deleting partitions. In short, data loss occurs when going from dynamic to basic; not when going from basic to dynamic. Dynamic disks are divided into 5 types.
a. Simple Volume: a single volume on a single disk.
b. Spanned Volume: built with at least 2 and at most 32 disks. Data is written sequentially across the disks. When the first disk fills up the writing continues on the next disk. If any disk fails, only the data on that disk is lost. As data is written and read sequentially, slowdowns are minimal. Used to expand capacity when space runs out.
c. Striped Volume: known as RAID 0. Can also be done with a single disk. Supports up to 32 disks. Data is split into 64 KB blocks and written. This gives maximum performance. If one disk fails, all data is lost.
d. Mirror Set Volume: known as RAID 1. Built with exactly 2 hard disks. Mirroring means writing the same data to the other disk. Because data is written simultaneously, write performance can suffer. Reads are not affected because only one disk is read. If one disk fails, the data is still available on the other.
e. RAID 5: built with at least 3 and at most 32 disks. RAID 5 is sized by the smallest disk. Data is written in 64 KB blocks. With 3 disks, 64 KB data is striped across 2 disks and parity is written to the third. Therefore the size loss equals the size of one disk. If one disk fails, the others contain its data so there is no data loss. If 2 disks fail, all data is lost. Write speed is slow, read speed is high.
Disk-1 Disk-2 Disk-3 64 KB Parity 64 KB Parity 64 KB 64 KB 64 KB Parity. RAID structures are implemented in two ways.
1. Software RAID: built inside the OS. RAID 0, RAID 1 and RAID 5 can be built with software.
2. Hardware RAID: built without OS support using hardware. Requires a RAID card. RAID 0, RAID 1 and RAID 5 can be built. These can also be combined.
RAID 10 (RAID 1+0). Writes are slow, reads are at normal speed.
RAID 15 (RAID 1+5). Also known as RAID 6. 2 disks are mirrored (RAID 1). 3 disks are striped with RAID 5. So at least 5 disks are required.
For example, HP servers ship with a Smart Start CD that builds hardware RAID. Boot the server with the CD before installing the OS. Enter “Configure array”, select disks and RAID type. After RAID setup go to Deployment Services and insert the OS CD to begin installation.
On basic disks, disk information is written to the registry.
On dynamic disks the info is stored on the disk itself in a 1 MB area; therefore dynamic volumes cannot be smaller than 1 MB. Dynamic disks appeared with Windows 2000 Server.
Hot Swap: ability to remove a disk while the computer is running. There is no need to shut down the PC to replace a failing disk. Just plug in the new disk and rescan.
64-bit operating systems support up to 128 primary disks. 32-bit OSs support up to 2 TB disk size, while 64-bit OSs support sizes above that.