Following up on RAID Level Zero
This is a response to some of the comments made about the previous posting on RAID Level Zero and includes some expert commentary.
My previous posting (Don't get burned by RAID Zero) on RAID Level Zero was a warning - both that it can be dangerous and that you may inadvertently be using it.
To make an analogy, consider the old joke regarding the purchase of a yacht. The potential buyer asks how much the yacht costs and the seller responds "If you have to ask, you can't afford it." In the current context: if you don't know what RAID Zero is, you shouldn't be using it.
But, the devil is in the details.
The danger with Raid Zero lies in the fact that every file is split between two hard disks and if either fails, you lose all your data. Thus, despite some reader comments to the first posting, your odds of being victimized by a hard disk failure are twice those of someone using a single hard disk. Like a lottery drawing, you have two balls in the hopper.
The hardware device that keeps track of where to store each half of a file is called a controller. If this controller fails, you again lose all your data, even though each hard disk may be alive and well. Your data is there, but without a road map, it can't be found.
A reader disagreed, saying that a Raid Zero controller can simply be swapped out for a new one and your data is not lost. This is not the case.
For one, external hard drives, whether they have one or two internal disks, are not meant to be user serviced. And, it turns out all Raid Level Zero controllers are not the same.
Ontrack Data Recovery
For help with the issue of replacing a RAID Zero controller, I turned to a company famous for being world class experts in hard disks - Ontrack Data Recovery.
If you are not familiar with them, Ontrack is a vendor of last resort. That is, when all else fails and you absolutely must recover the files on a malfunctioning hard disk, call Ontrack. And, to repeat the joke above, if you have to ask how much their services cost, you're data files are not that important.
Jeff Pederson, Manager of Data Recovery Operations for Ontrack Data Recovery, weighed in on the issue of replacing one RAID Zero controller with another:
As a typical engineering response to your question of whether all raid level zero controllers are exactly the same, my answer is that they are and they are not. Obviously the way that they are all alike is in how essentially they stripe data between disks, but they are not all alike in how they go about accomplishing that task.
As far as the next question of difficulty and expense related to recovering from a raid controller failure, Ontrack has developed tools to overcome any major technical difficulty so we can usually overcome nearly every scenario related to raid failures, whether the problem is one or both of the drives have physically failed, the raid controller was reinitialized and it does not recognize the original volumes that were on the disks, or even when data has been re-written to the raid 0 after a re-initialization we have been successful in recovering underlying data as well.
As far as the commenter indicating that if the controller fails, all the data is lost, that is right up our alley and is completely untrue. We have recovered data from Raid 0, 1, 3, 4, 5, 10, 50, etc.
As with most of these situations if customers contact the controller manufacturer to discuss their particular situation with them, there are ways for controllers to be replaced and have them identify the original raid configuration if the drives are still operational.
It's fair to say, that if the RAID Zero controller fails, you're in deep trouble.
This is in stark contrast to hard disks connected to normal ordinary controllers, be they IDE/ATA or SATA. These controllers do indeed all function in the same way and, should one fail, it's a fairly simple thing to connect a hard disk to another one.
Scott Meuller
In the original posting, I mentioned a failed LaCie external hard drive with two internal hard disks, configured as RAID Zero. This was the first time I'd run across an external hard drive, being sold as a single unit (as opposed to a NAS device), with two internal hard disks. Scott Meuller, who was nice enough to add his thoughts on the subject, has been warning people about problems with this design all along (see Got a BIG drive? Then where do you keep the other two?). Quoting:
"... while their designs and shortcomings are obvious to a professional, virtually none of the published product reviews I've seen point out the multiple internal drive/RAID 0 configuration or the potential ramifications."
As for the failure of the RAID Zero controller in one of these units, Scott says it might "be possible to swap the otherwise standard internal drives over to another identical unit in order to restore array functionality (recover the data)."
When it comes to PC hardware, Scott Meuller literally wrote the book on it. Hordes of techies learned the ins and outs of hardware from his line of Upgrading and Repairing PCs books. If he isn't sure how to deal with this problem, it's not one you want to be faced with.
Never mind, that to have an "identical unit", you likely have to have purchased both at the same time.
Other Reader Comments
Many comments on the initial posting mentioned backups as a cure for data loss from a hard disk failure, RAID or no RAID. There will be many postings on this blog in the near future about backing up data on a computer. It's inherent to Defensive Computing.
Thanks to ajhoughton for helping to make my point.
To MC: what is LDO?
Update: July 15, 2007. While browsing the web site of Gateway Computers today, I happened to notice that they offer RAID Zero as an optional feature on the FX530XG computer. Quoting Gateway: "Experience pure power with optional RAID 0 with SATA II/300 drive support for improved performance."
- Original posting: Don't get burned by RAID Zero
- Comments on the original posting