Many different technologies have been created to help reduce the chances of data loss.  It has been openly accepted that there is no perfect storage medium; yet, many technicians will use RAID 5 and swear by it.  The idea of having two points of failure seems like a safe bet, providing that the drives don’t go through a common catastrophic event.  However, it does seem odd that if RAID 5 were a sure bet, why do banks, hospitals and universities do nightly backups of their RAID 5 servers with high end SCSI hard drives?

With the introduction of drives measured in Terabytes, home and small business users are turning to low end SATA systems and setting up 2TB RAID 5 servers.  Most of these users don’t backup these systems because they don’t know how and it just takes too long to copy 2TB of data accross a network.  So, all their precious personal and business data sit on drives that are just not designed to be in such critical situations.  When disaster strikes, the users find themselves at a loss and being quoted hefty fees for professional data recovery services.

The problem with RAID 5 and larger drives is that the odds of a drive forming a single bad sector is exponentially increased with the size of the drive.  The means that a 2TB drive will likely form at least one bad sector within its first years of use.  This is usually not an issue, as the new drive’s of today have built in processess to remap those sectors as they come into being.

The problem lies in how a RAID 5 system works.  When a drive fails, the system uses a parity bit to deduce the missing sectors from the missing drive.  When the defective drive is replaced, the RAID system rebuilds the drive, using the information from the other working drive.  But, if one of those drives have a single bad sector, the RAID rebuild fails and the user is left with a big mess.

What does this mean?  Don’t use RAID 5?  No, that is not what we are saying; though, it might be better to use RAID 6 or 10, systems that have two points of failure.  It is more important to have your data backed up in mulitple locations than to have redundancy in one.  That is, instead of using three 1TB hard drives and setting up a 2TB RAID 5, you could use one 1TB drive for your data and alternate between the other two 1TB drives for regular backups.