Hardware failure can be a show stopper for any shop without proper backups, and hardware reserves. It can be very costly to send hard drives for data recovery. Even with a proper backup plan in place, failures can happen.

To mitigate some of the headache, and expense in drive recovery, and downtime. We highly recommend data replication to another node, or volume replication to another DSS node be deployed. With replication in place, a real time picture of the data can be maintained, and used if equipment should fail.

As an example, if a harddrive fails in the RAID, it can take days to rebuild, potentially causing file issues on volumes if the controller fails the rebuild. This can affect file systems, as well as data on the volumes. Even after a successful rebuild, data can be lost, and unrecoverable through any user action. This can cause long downtimes, and inaccessible data.
Using Data/Volume Replication, and a good sound backup stategy, this can be avoided.

We highly recommend a good strategy be followed. If you require assistance, please feel free to ask in our forums, or through the proper support channels for your product.
More information can also be found at our blog.
Various RAID levels, and informartion can be found here. Be aware any RAID level does not promise there will be no data loss, and this is why its important to have a plan in place to backup either on or off site.
Even the most simple of backup solutions can help, even just an external USB harddrive can be utilized as a dynamic volume, with vitrual tapes from inside DSS.