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First time setting up a RAID, need help

S

stuuke

macrumors regular
Original poster
Apr 19, 2004
240
51
I am trying to set up a RAID configuration and wanted to confirm that I am doing it correctly.

I purchased two Seagate 400gb IDE drives and have them in a two bay USB 2.0 enclosure. The enclosure is supposed to allow both drives to be set to master. I am setting them up to use with my Macbook Intel 2.0 running 10.4.6.

If I understand correctly all I have to do is use the disk utility and drag both hard drives to the RAID setup. I planned on using a RAID 1 for mirroring. Is there anything else I need to do? Once completed what do I need to know about using the drives? It is my understanding that if one drive is altered it automatically has the other drive duplicate once it is activated.

Any help or suggestions would be appreciated. Thanks.
 
Sounds like you have it correct in your head. What you are doing is a software RAID, which will achieve the redundancy, but does produce an overhead on your CPU. Since the write command is sent from the computer itself to each hard disk, you may also find that at times the USB bus gets congested with the write traffic, so don't get frustrated if you find performance can sometimes be slow. I know you already have your enclosure, but for anyone else reading the thread, you can get USB hardware RAID systems that remove the USB bottleneck by mirroring the write request inside the enclosure itself. Here's an example of such a device.

However, saying that, software RAID is pretty automatic once you've configured it. Both drives will get write updates, and either drive will respond to a read request.
 
Will it slow down performance only when accessing the drives or is it constantly slower? Is there any better combination that won't take 50% of my hd space?
 
Another question I had is can I put a different drive in the enclosure and then replace it with the RAID drive after I'm done using it?
 
It will only slow down performance when writing to the drive, and you'll only notice it when the file size is large enough. When reading, it will actually be slightly faster than having one drive since roughly half the data will come off each, so the drive heads don't have to move so much.

Not sure on your other question. I suspect that if you replaced one half of the pair, OSX would mark it as a failed mirror but still allow you to access the data on the remaining half. You would need to completely re-mirror the second RAID drive when you put it back in the enclosure though which will take a while. The question is:- When you put your new drive in the enclosure, will OSX automatically attempt to build it as the new mirror for the RAID drive that's still there? That one I don't know the answer to I'm afraid, but FWIW I wouldn't recommend doing it.
 
Before you populate your new RAID 1 (mirrored) array with valuable data, I suggest doing a trial run with junk data.

1. Set it up as in your original suggestion.

2. Copy some data you don't mind loosing, e.g. from a DVD or something, onto your new RAID array. At least a couple of gig.

3. Shut down and pull out one of the drive cables to stimulate failure.

4. Restart and see if you can still access the data on the remaining drive. Can you use it as a single, normal drive, i.e. put more data on?

5. Shut down and reconnect the missing drive. See what happens when you restart, if the two drives are now in different states.

6. Recreate the RAID, remove a drive again, and erase (format) it, and then reconnect it as part of the RAID. Does it auto rebuild the RAID? What actions do you need to take to repair the RAID?

Once you've done all that, you'll have full awareness of what to do when (not if) a drive fails.

Hope that helps.

I have my own problems with setting up a RAID 5 system, and I think I've been caught out quite badly. See https://forums.macrumors.com/showthread.php?p=2562181

Help would be appreciated.

Thanks

..RedTomato..
 
You know that USB requires the machine's CPU to manage the disk access, right? So you are going to do a Software RAID (which requires the machine's CPU to calculate the writing of the data) onto TWO USB drives (which BOTH require the CPU to babysit them)... I think you're fixing to have the slowest RAID system in the civilized world, friend. I would NOT rely on this system for diung video or audio capture or playback, or any task that relies on consistent uninterrupted CPU cycles...
 
If it's that bad then why is Mac set up to do it that way?
 
For some people, the reliablity is worth the slowness.

It's a hell of a lot more reliable than a single HD, and a hell of a lot more convient than regular backup to floppy / DVD / tape which were your only choices before.

DVD/ tape backup is still useful tho as RAID doesnt protect against viruses / user error as pointed out above.

.. RedTomato..
 
Maybe I should explain my needs so that I can get the most accurate answers. I currently have two external drives, a 125 and a 250 gb lacie. I am a photographer and my files are constantly growing in size. I bought 3 Seagate 400gb drives one of which died the first week I had it. I have the 2 bay enclosure I mentioned for them. I may do some video work but manly I am just looking for a safe way to backup my photography assignments. Would I be better off selling off the system I got and getting the built in Raid? I work from a laptop so internal drives or cards for my current computer are not an option. Thanks for you help in advance.
 
It's all a matter of degree.

Two drives in one cabinet is fine for RAID 1 -- except you have a single point of failure around the power supply. It goes, and your drive and its mirror are both offline -- or fried. I have already said my piece about USB performance and CPU loading.

Seriously, I would get
1) a Firewire hub (or combo USB/FW hub) so that you are not plugging directly into the 'Book
2) two separate Firewire enclosures instead of the 2 bay USB

Then go ahead and set up the software RAID.

A quality Hardware RAID enclosure might be better (Wiebetech, Granite) but they are %*#* expensive.

If you had a MacBook Pro or Powerbook 15"/17" another option would be a card with Firewire or SATA to drive the drives, reducing even further the bandwidth limitation of the Firewire port.
 
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