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 Post subject: Got a BIG drive? Then where do you keep the other two?
 Post Posted: Tue Jul 10, 2007 1:56 pm 
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Recently I was asked a question regarding this blog post:

Quote:
If a raid level zero controller fails in an external hard disk, its pretty much fatal. I've spoken to Ontrack and LaCie about this. If however, a raid zero controller is a PCI card on the motherboard and easily swapped, can the data be recovered (assuming the disks themselves are OK)?

I have cautioned people about "double-drives" like some of the LaCie units ever since they first appeared. Their RAID 0 internal design (and resultant shortcomings) were immediately obvious not only due to the size of the units (big enough to fit two 3.5" drives internally), but especially due to the fact that they were being offered as xxxGB "drives" when I *knew* that drives of only half that capacity were available on the market. Unfortunately 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.

However, while these devices may have some shortcomings, if the internal controller or other circuitry fails, it *should* or at least *might* be possible to swap the otherwise standard internal drives over to another identical unit in order to restore array functionality (recover the data). This scenario could be easily tested by purchasing two identical units, loading them with different data, and then simply swapping the drives between them. If the data were readable after the swap, then a similar recovery after failure should be possible as well. Other factors may be involved, for example the donor unit may need to have the same internal circuit or firmware revision for this to work, meaning that units which seem identical on the exterior may not be identical at all. Likewise it should be possible to replace a failed RAID controller (or motherboard with integrated RAID controller) with an identical unit, recovering the array (and data) as well.

But recovery is a last, last resort, the main issue here is backup: While I don't normally recommend RAID 0 for data storage due to the increased risk of failure, that risk is essentially immaterial with respect to data loss. Perhaps a better title for the entry might be: "Don't get burned by a failure to backup", as those clients were not "burned by their inadvertent use of RAID 0", instead they were burned by their *advertent* failure to backup their data! They apparently failed to understand that ALL data that is not backed up is subject to instantaneous and total loss.

They are unfortunately not alone. Few individuals seem to understand the need for backup, which is becoming even more of a problem in these days of terabyte hard drives. Years ago I was a proponent of tape backup, as multiple tapes would allow one to easily and inexpensively make the requisite minimum two backups of important data (with one of them ideally stored off-site). But that was in the days when the capacity of tape storage maintained parity with the capacity of disk storage.

Today the only thing I know of that can easily and inexpensively backup a large drive is *another* drive of equal (or greater) capacity.

And of course one backup isn't enough, as in that case when a failure occurs you would be running without backup from the time of the failure until the repair and restore were completed. Any subsequent failure during *that* time could mean total loss. This means at a minimum that a second backup is required in order to be protected over the duration of a storage failure.

Bottom line: RAID at any level is no substitute for backup. I recommend storage volumes or devices be acquired in *triplicate* (at a minimum). That means if you use a device (or array) containing a volume with xxxGB of capacity, then you should insure that you have at least two additional separate physical devices containing volumes with the same (or greater) capacity, with the extra two used solely for backups.

The next time somebody shows you their monster size drive or array, ask them where they keep the other two? <g> Scott.


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