In block striping, the total disk capacity is equivalent to the sum of the capacities of all drives in the array. This combination of drives appears to the system as a single logical drive. RAID 0 provides the highest performance. It is fast because data can be simultaneously transferred to or from every disk in the array. RAID 1 implements disk mirroring , where a copy of the same data is recorded onto two drives.
go By keeping two copies of data on separate disks, data is protected against a disk failure. If, at any time, a disk in the RAID 1 array fails, the remaining good disk copy can provide all of the data needed, thus preventing downtime. In disk mirroring, the total usable capacity is equivalent to the capacity of one drive in the RAID 1 array.
Thus, combining two 1-Gbyte drives, for example, creates a single logical drive with a total usable capacity of 1 Gbyte. RAID 3 implements block striping with dedicated parity. This RAID level breaks data into logical blocks, the size of a disk block, and then stripes these blocks across several drives.
One drive is dedicated to parity. In the event that a disk fails, the original data can be reconstructed using the parity information and the information on the remaining disks. In RAID 3, the total disk capacity is equivalent to the sum of the capacities of all drives in the combination, excluding the parity drive. Thus, combining four 1-Gbyte drives, for example, creates a single logical drive with a total usable capacity of 3 Gbyte.
This combination appears to the system as a single logical drive. RAID 3 provides increased data transfer rates when data is being read in small chunks or sequentially. RAID 5 implements multiple-block striping with distributed parity.
This RAID level offers redundancy with the parity information distributed across all disks in the array. Data and its parity are never stored on the same disk. In the event that a disk fails, original data can be reconstructed using the parity information and the information on the remaining disks. The following table provides a description of the advanced RAID levels.
The external RAID controllers provide both local spare drive and global spare drive functions.
The local spare drive is used only for one specified drive; the global spare drive can be used for any logical drive on the array. The local spare drive always has higher priority than the global spare drive. Therefore, if a drive fails and both types of spares are available at the same time or a greater size is needed to replace the failed drive, the local spare is used.
If there is a failed drive in the RAID 5 logical drive, replace the failed drive with a new drive to keep the logical drive working. A local spare drive always has higher priority than a global spare drive; that is, if a drive fails and there is a local spare and a global spare drive available, the local spare drive is used.
A local spare drive always has higher priority than a global spare drive; that is, if a drive fails and both a local spare and a global spare drive are available, the local spare drive is used. The 9-Gbyte local spare drive aids logical drive 0 once a drive in this logical drive fails. If the failed drive is in logical drive 1 or 2, the 4-Gbyte global spare drive immediately aids the failed drive.
All rights reserved. RAID Basics. Mirroring and striping. Striping with dedicated parity.
Striping with distributed parity. Striping of RAID 3 logical drives.
Raid of the Ratskull Rodents is a book full of different and challenging vocabulary, but rather than let readers be baffled by this, I have highlighted certain vocabulary in bold, then provided definitions in footnotes at the bottom of the page. I hope this will be a feature that young readers will really appreciate.
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