Henry Newman opines over at EnterpriseStorageForum.com about the current state of RAID, and where we may be headed next
…In my opinion, RAID-6 is a reliability Band Aid for RAID-5, and going from one parity drive to two is simply delaying the inevitable. The bottom line is this: Disk density has increased far more than performance and hard error rates haven’t changed much, creating much greater RAID rebuild times and a much higher risk of data loss. In short, it’s a scenario that will eventually require a solution, if not a whole new way of storing and protecting data.
So, what’s a mother to do?
The disk reliability density problem is getting worse, and fast. Some vendors are using techniques such as write logging — keeping track of write on another disk during rebuild to allow the rebuild to occur faster — to get around the growing problem. Will this solve the problem for the long term, or is this the equivalent of the RAID-5 to RAID-6 fix that just delayed the inevitable problem? Personally, I think it will turn out to be just another short-term fix. The real fix must be based on new technology such as OSD, where the disk knows what is stored on it and only has to read and write the objects being managed, not the whole device, or something like declustered RAID. In essence, the disk drive layer needs to have more knowledge of what is storage, or fixed RAID devices must be rethought. Or both.
There are some technologies that are available today and on the way that could help alleviate the problem. The sooner they arrive, the better chance we have of avoiding MTDL.