What is the best way to RAID external drives?

I love the fact that you can now buy 1 and 2 TB drives cheap. However that much data on a single drive scares me. What would be the best way to build a raid system out of external drives? I am looking for advice on performance, price, and ease of data recovery should a drive fail. What do I need besides the drives? How many drives should the raid be? Any advice is appreciated. - Thanks.

Solution 1:

This kind of depends on what you're trying to keep redundant and what degree of safety you want, and what exactly you're looking for in "safety" (just availability? Redundancy? Backup?)

RAID isn't backup...

And RAID doesn't help beyond drive failure. If you have a controller failure you're going to have an availability issue.

Beyond that there's consideration in that external hard drives often have things like power and heating issues if you're going to use them 24/7. Many work fine, but some do have issues with this, since they're meant to be used for portability and not as a workhorse drive (people used to play with making older iPods into RAIDs and discovered the drives died sooner, also I've read of external drives that would try to power down at inopportune moments and have spin-up issues).

If you're a home user just looking for some RAID setup for some important home data and not customer or business data, I'd look at getting a cheap computer with a couple large drives and turn it into a NAS device with something like FreeNAS. It becomes a network appliance with a web interface for configuring it. Then set it up with mirroring.

Also there are papers out there warning about the dangers of RAID (if you really want heavy-duty stuff) and large disks now, because as drives get bigger it's becoming more likely that you'll hit the point where you will have a drive failure in a cluster and not know it until you're trying to recover from a total drive failure (i.e., you have RAID 5 with three disks, a drive fails. You slap in a new drive to replace drive C. As the volume recovers data from A and B to rebuild C, the system discovers an unreadable spot on drive B. You can't recover the volume because of that bad bit, undetected before, so your volume is hosed if you don't ALSO replace drive B and therefore ruin the RAID volume and then recover from a complete backup; we had this happen to us with a Dell PERC-backed RAID 5. Trust me. It sucks. And with drive sizes increasing to ridiculously huge sizes this is more and more common, leading people to recommend RAID 10 or better if you're running servers that need to be available as much as possible and downplaying using RAID 5). One link that I read before is found here discussing RAID 5 for small businesses (don't use it!).

In other words...playing with RAID at home is fun and can be useful, but overall it won't gain you much unless you have a specific purpose behind it.

Another thing to consider: if you're not using hardware RAID like 3ware's cards, you're going to have more difficulty figuring out which drive is dead unless you have a system in place for knowing that drive A is labeled , so when the RAID system you're using goes ploof you can figure out which physical drive is the issue and swap the RIGHT one. Many hardware controllers for RAID will have blinkies to warn you of drive giving problems. For software raid, it can be a crapshoot unless you have a plan ahead of time.

If you have data that you need to be careful to keep available, I'd look first at backup strategy. RAID is useless there. If you delete your important doc in RAID it's gone immediately. If someone hacks it, it's gone immediately. If something corrupts it, RAID will dutifully duplicate the corruption. RAID is only good for being able to use the system if something fries a drive or if you're looking to play with performance with RAID 0. Backups are what can save your bacon when a system fries or data corrupts.

Oh...and depending on how you configure all this and how your budget runs...adding lots of external hard drives can up your electric bill more than a cheap system with internal hard drives running NAS software to turn it into an appliance :-)

Solution 2:

You can buy one of those NAS units, which are purpose built for this sort of stuff, and set it up in RAID6 or RAID10 if you want redundancy, so even if a drive fails you can replace it and rebuild it with relative ease.

This pretty much defeats the purpose of having an external HDD though, as it is hardly considered portable, and if you need to move data around from A->B it is assumed that you will still have this data available on either A or B.