One of the more common requests that we receive here at Tierra is for RAID 0 recovery. It is often the case that those clients who need it did not even realise that they had this configured in the first place. We usually encounter this configuration on external hard drives which (often unknown to the users) house two physical hard disks within the chassis.
The user will usually be able to tell if they have this type of external storage device when they plug it into their PC or Mac for the first time. It will normally be the case that they will be prompted to select between “striped” or “mirrored” format. This is the external device asking how the owner wishes the two physical drives within the external storage device to be setup. “Striped” can be given the more technical designation of RAID 0 and “mirrored” that of RAID 1.
Striped or Mirrored, Which Setup is Best?
If the user opts for striped then each file that you save to the external device will be split between the two hard disks inside. In other words part of the file will exist on one of the drives and part on the other (for a more complete explanation of how this works look at our Dummies Guide to RAID). This is done in order to achieve faster read and write times. The two halves of the file are simultaneously accessed on both disks making access times faster than would be the case if the file was stored on a single drive. It should be noted however that people are often disappointed with the speed performance of striped data stores. The reason for this is that the speed differences are likely to be noticeable only when working with large file sizes. The most likely beneficiaries are graphic designers and people working in similar roles because they are routinely working with graphic files sized in the tens of MB. Ordinary users are likely to find that the speed difference is negligible. Never forget however that this type of recovery is necessarily more complicated than recovery of the same files from a single physical hard drive, not only must both drives be accessed but the data must then be put back together, somewhat in the manner of a jigsaw puzzle.
The other option, RAID1 (or mirrored) will write each file twice, once to each of the hard disks. This of course means that only half of the advertised space is available. Take the example of an external sold as a 1TB model. It will house two 500GB units. If configured as RAID0 the full 1TB space will be available, however if level 1 is chosen there will only be 500GB. The benefit is that it does not expose the owner to the same risk of needing recovery work. If one drive fails then files and folders should still be safe on the other. Again it is worth noting that level 1 does not necessarily offer all that it appears to at first. If a write error causes file system corruption and subsequent loss of access to files, then both drives will be simultaneously corrupted. In other words level 1 will protect against some causes of data loss but not others. Make no mistake however, although it requires a high cost in terms of lost storage space, if the information you will store on this device is critical the need to avoid being in the position of requiring rescue work should be the deciding factor for you.
Why Are Striped Drives More Vulnerable?
In essence, by configuring the two physical drives as RAID level 0 you have effectively doubled the risk of losing access to your files through hard disk failure. Each of your files now exists in part on one of the drives and in part on the other. Therefore if either of these disks fails, you will lose access to all of your documents. Professional file retrieval is likely to be your only hope once you are in this position.
Some manufactures do go to the trouble of ensuring that the potential risk to your data of using level 0 is clear (such as this excellent example from a Lacie setup manual):
However, many do not make it clear and then owners simply focus on the loss of storage space which accompanies the alternative.
In summary, if you routinely work with large files then RAID 0 does make sense for you as you will notice faster read access. However, remember that recovery from this configuration forms a regular diet for professional recovery experts. Ensure that you take appropriate measures to back-up any documents that you store on your striped external drive.