RAID Configuration overview

A Redundant Array of Independent Drives (or Disks), also known as Redundant Array of Inexpensive Drives (or Disks) (RAID) is an term for data storage schemes that divide and/or replicate data among multiple hard drives. RAID can be designed to provide increased data reliability or increased I/O performance, though one goal may compromise the other. There are 10 RAID level. But which one is recommended for data safety and performance considering that hard drives are commodity priced?
I did some research in last few months and based upon my experince I started to use RAID10 for both Vmware / XEN Virtualization and database servers. A few MS-Exchange and Oracle admins also recommended RAID 10 for both safety and performance over RAID 5.

Quick RAID 10 overview (raid 10 explained)

RAID 10 = Combining features of RAID 0 + RAID 1. It provides optimization for fault tolerance.
RAID 0 helps to increase performance by striping volume data across multiple disk drives.
RAID 1 provides disk mirroring which duplicates your data.
In some cases, RAID 10 offers faster data reads and writes than RAID 5 because it does not need to manage parity.

Fig.01: Raid 10 in action

RAID 5 vs RAID 10

If a drive costs $1000US (and most are far less expensive than that) then switching from a 4 pair RAID10 array to a 5 drive RAID5 array will save 3 drives or $3000US. What is the cost of overtime, wear and tear on the technicians, DBAs, managers, and customers of even a recovery scare? What is the cost of reduced performance and possibly reduced customer satisfaction? Finally what is the cost of lost business if data is unrecoverable? I maintain that the drives are FAR cheaper! Hence my mantra:
NO RAID5! NO RAID5! NO RAID5! 

Is RAID 5 Really a Bargain?

Is RAID 5 Really a Bargain?":

• RAID 5 costs more for write-intensive applications than RAID 1.
• RAID 5 is less outage resilient than RAID 1.
• RAID 5 suffers massive performance degradation during partial outage.
• RAID 5 is less architecturally flexible than RAID 1.
• Correcting RAID 5 performance problems can be very expensive.

RAID arrays configuration

To make picture clear, I'm putting RAID 10 vs RAID 5 configuration for high-load database, Vmware / Xen servers, mail servers, MS - Exchange mail server etc:

RAID Level	Total array capacity	Fault tolerance	Read speed	Write speed
RAID-10 500GB x 4 disks	1000 GB	1 disk	4X	2X
RAID-5 500GB x 3 disks	1000 GB	1 disk	2X	Speed of a RAID 5 depends upon the controller implementation

You can clearly see RAID 10 outperforms RAID 5 at fraction of cost in terms of read and write operations.

A note about backup

Any RAID level will not protect you from multiple disk failures. While one disk is off line for any reason, your disk array is not fully redundant. Therefore, old good tape backups are always recommended.