Question : Problem: Can someone explain Raid and Mirroring on Servers.

What is Raid 5, Raid 10, Raid 0, Raid 1, etc?  

I read this somewhere:

The practical advantage in operation is that you can remove individual drives from the system to the exclusion of others without interrupting server operation, and then insert a replacement drive.

How can you replace a drive without losing the data that was on it?  Is all data mirrored?

Thanks

Doug

Answer : Problem: Can someone explain Raid and Mirroring on Servers.

RAID or "Redundant Array of Inexpensive Disks" is a storage technology which is primarily used to provide two things, the first being Redundancy and the second Performance. RAID can provide other advantages but these are the main ones.

Let's deal with Redundancy first.

Redundancy is simply the quality which allows part of a system to fail without impacting on the systems overall functionality. In a RAID (Please never refer to a "RAID array" which is a term almost as annoying as an "ATM Machine) multiple disks are used to provide redundancy

RAID 0
No redundancy in this configuration, but allows for the best performance because of it.  Fastest write performance of any RAID configuration.
At least 2 hard disks are required, usually of the same size and speed.
Size is equal to the smallest hard drive in the RAID * the number of drives.

RAID 1
Also referred to as “mirroring”.  Redundancy is is acheived by writing identical data to both drives.  If one drive fails, the other drives has all your data.
Requires 2 and only 2 hard disks.
The size of the array is the size of the smallest drive in the array.
Commonly used for operating systems.

RAID 3 (Almost never used any more)
In an R3 configuration, data gets striped across multiple disks at the byte level.  A single disk is used to store parity information and the failure of any one disk, including the parity disk, will not cause failure of the array.  The major bottleneck in this solution is the single parity disk, which much be accessed every time information is written to the array.
Requires at least 3 hard disks.  2 for storing data and 1 parity drive.
Size of the array is equal to the size of the smallest drive * (total number of drives – 1)  

RAID 4 (Almost never used any more)
Same as RAID 3, but the data is striped in block and not bytes.  This improves the performance of reading data.

RAID 5
This is the most popular RAID configuration for storing data, such as your database files.  Unlike RAID 3, parity information is striped across all disks in the array, just like the rest of the data.  This gives R5 a performance increase over R3 when writing data.  Like RAID 4, it uses block level striping for improved read performance.  Fault tolerance is maintained by making sure that the parity information for any particular block of data is not written on the same drive that contains the actual data.
Perfect for storing of data where the majorty of access to the RAID will be read access, especially when configured with smaller stripe sizes.
Requires at least 3 hard disks.
Size of the array is equal to the size of the smallest drive * (total number of drives – 1)

RAID 6 same as RAID 5, but parity information is written twice.  The difference in R5 and R6 is improved fault tolerance, but with a performance hit.

RAID 10 this is simply a combination of RAID1 and RAID0