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.
RAID 5 vs RAID 10
From Art S. Kagel research findings:
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! NO RAID5! NO RAID5! NO RAID5! NO RAID5!
Is RAID 5 Really a Bargain?
Cary Millsap, manager of Hotsos LLC and the editor of Hotsos Journal found the following facts - 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.
My practical experience with 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|
500GB x 4 disks
|1000 GB||1 disk||4X||2X|
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.
Please add your thoughts and experience in the comments below.
- Battle Against Any Raid Five initiative - A website dedicated to RAID related issues.
- RAID article from the wikipedia - Provides tons of information about both standard and non standard RAID levels.