RAID i.e. Redundant Array of Independent Disks, is a mechanism which enhances the speed, storage capacity & reliability of your webserver using more than one hard disk instead of the traditional single hard disk solutions. In essence, RAID actually works in such a way which allows the multiple hard drives present on the machine to be combined and used as one big hard drive with different levels of benefits and also covers your risk of data loss. The higher your RAID level, the better risk coverage you get. Completely subjective to your need for data safety and redundancy, you can use several variations of RAID depending on your budget. RAID solutions are available starting from as low as $40.00 to a few thousand $$. There is no such thing called as the best RAID combination or implementation. What RAID levels you need is completely dependent on the applications, processes and softwares which run off the server.
Previously, RAID could be implemented and coupled with only the high end and most expensive server configurations. Now-a-days. with the advancement in technology and the vast amount of research which has been done on RAID, affordable yet effective RAID controllers have been made which can be easily procured and used. There are different RAID levels which exist.
Software Raid 0
This is not something we should be recommending but you will be asked about it. With Raid 0 you take two hard drives and turn them into 1 big HDD. This improves the storage space and performance but there is NO fault tolerance. If one of these drives were to fail, all data would be lost. There would be no option for recovery. If a client asks you about this, make it very clear that you do NOT recommend it.
Hardware Raid 1
This is an option for 2 hard drives and is highly recommended. Raid 1 offers a slight performance increase and also allows for any 1 of the drives to fail without the server crashing or data being lost. The main benefit of raid 1 is the cost. It’s relatively cheap to implement and can be offered to clients with a low budget. If a client was to have 2×250 GB hard drives in Raid 1, Only 250 GB would be available.
Hardware Raid 5
Raid 5 is slightly different from Raid 1 and Raid 10. Whereas Raid 1 and Raid 10 offer a slight performance increase, Raid 5 offers a much greater performance increase. Raid 5 contains a minimum of 3 hard drives. At any one time, any one drive can fail and the server will keep on working. If more than 1 drive fails, all data is lost. You may get people looking for game servers asking about Raid 5. If a client was to have 3×250 GB HDD in Raid 5, 500 GB would be available.
Hardware Raid 10
A Raid 10 array contains a minimum of 4 hard drives. In this configuration the drives are paired up and the data is mirrored. In theory, the server could sustain two hard drive failures and the server will keep on running. However, the server can not sustain two hard drive losses on the same mirrored pair. As an example, let’s say a server has HD0, HD1, HD2, and HD3. Four separate drives. In this example we will say that HD0 and HD1 are mirrored and HD2 and HD3 are mirrored. If HD0 and HD2 were to fail, the server would carry on running without data loss. If HD0 and HD1 fail, all data stored on HD0 and HD1 would be lost. Modern raid controllers are very efficient. At the first sign of any fault, on any drive, it will automatically declare it as faulty and will request the drive be replaced. Raid 10 doesn’t offer the same performance level as Raid 5, but is more reliable. This is highly recommended for clients with a high uptime requirement. If a client was to have 4×250 GB hard drives, 500 GB would be available.
Setup times for RAID depends on the level which one chose. Normally it takes between 24 to 48 hours, wherein the higher you go on the levels, the more time it takes for the setup to be done.
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This post was written by on September 3, 2008
