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Old May 11, 2010, 12:48 PM   #1
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Sorting my backups - RAID 1 vs JBOD?

I was reading online that RAID1 is not a very reliable backup method, and is primarily for speedy recovery, over true reliability.

I want to buy a dual-bay enclosure; something like the Icy Dock MB662UEAB-2S;


People say they the best thing to do is get 2 separate external drives and backup with one, and use the other to make a copy of the backup drive, so you have 2 separate drives.

Would it be fine to just to put 2x1TB drives into the enclosure, setup as JBOD then use Superduper to clone drive A onto drive B. Or is this not a good idea.

Also can I stick a single drive into the IcyDock now and buy a second one later, as im a little shot of money at them moment.

I got a 500GB old schol hardrive i could use for redundancy for the next 6 months, before i add a second drive into the enclosure.
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Old May 11, 2010, 05:26 PM   #2
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What you read about RAID1 is correct--it only protects against a single-drive hardware failure, and keeps you going without delay in that case. If, however, you suffer data corruption, a file gets accidentally deleted, or the controller fails, RAID1 is no better than a single drive. It's really mostly useful to people who need more uptime--for example, at work we run a RAID1 so that if a drive dies there's no visible problem form the user perspective while I get a replacement. But it's ALSO backed up to a separate drive, as protection for if the whole server blows up or when somebody deletes something important. (RAID1 also reads faster, if the driver you're using supports reading from both drives at once; writes are the same as a single drive.)

As for your question, JBOD in an enclosure like that with the automated backup you describe is better than RAID1, but not as good as two drives in separate enclosures. Thing is, if the drive enclosure itself blows up, it could very easily take both drives with it, meaning no protection at all. Similarly, if one drive dies violently, it could corrupt the data on the other on the same controller; this is less likely with SATA controllers than PATA ones that shared the same bus, but I've seen it happen once.

Having two separate enclosures means that if one enclosure goes bad in a violent way it's very unlikely to have any effect on the other. Not 100%, since they will be physically connected through the same computer, but a lot safer.

This is what I do at home--fast FW800 enclosure for online data, then a cheap USB2 drive for the backup, since speed really doesn't matter.

Of course, the safest thing of all is to have some sort of an offsite backup plan, to handle something like a lightning strike (which would blow up anything plugged in in the house), theft, or fire. Again, I keep a drive at my parents' house 20 miles away for just such an occurrence. That of course is a hassle, so an alternative would be an online backup service at least for critical files, though those have major speed issues.
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Old May 14, 2010, 10:39 AM   #3
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I forgot to say thankyou for this reply, it was very helpful;

i posted a follow up here

(unibody) Macbook Pro 17'', 2.66 GHz, 4GB RAM, 320 GB HD (5400)
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