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You are here: MacNN Forums > Hardware - Troubleshooting and Discussion > Consumer Hardware & Components > Is it possible to RAID two external Drives

Is it possible to RAID two external Drives
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NDBounce
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Oct 30, 2008, 11:37 AM
 
I am hoping to put all my media (~400GB movies/music, etc) on to one media drive. My fear, of course is that Hard Drives die. I am trying to determine the best solution to do this. Currently I have 1 320GB HD, and 2 80GB Hard drives. 2 of the drives have USB/FW 400, and one has USB only.

My question is can I buy two new 500GB internal drives, and then put these drives into two of the enclosures I have (probably the FW enclosures) and RAID the two external FW enclosures in a RAID 1 config so that if one drive goes bad, I do not lose my media.

If this is possible, can someone please give me step by step instructions on how to RAID two external FW drives.

Thank you,

O
B unce!
     
turtle777
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Oct 30, 2008, 12:58 PM
 
I think Disk Utility can create "virtual" volumes, combining multiple volumes into one. I have never done it though.
This would be comparable to a RAID 0 solution. I would not do this myself, as you are combining multiple disks, and the slowest of them is gonna determine the overall performance. Plus, if one of them goes bad, any disk tools will have a hard time recovering anything off of it.

I don't think you can just RAID 1 two external drives.

If I was you I'd by a big drive and make it the Time Machine disk. Then you can back up multiple smaller external disks to it. In fact, that's exactly what I did with the 2 TB drive I bough a month ago.

-t
     
Spheric Harlot
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Oct 30, 2008, 02:37 PM
 
Using Disk Utility, you can very easily create a mirror RAID out of two external disks.

In Disk Utility, just click on the "RAID" tab, set the type of RAID you want, and then just drag the drives you wish to use to that area.

I have had two 250GB LaCie drives running as a mirrored RAID for over a year now.

If one disk is disconnected or dies, it will automatically be re-synced with the remaining volume.

For further info, see the Disk Utility help menu.
     
SSharon
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Oct 30, 2008, 05:23 PM
 
Even a mirror RAID is not a real backup, it is for redundancy only. If data gets corrupted on one drive it is corrupted on the other. If you accidentally delete a file on one drive it is gone off both.

I would have your media backed up to each drive separately and not use a mirror raid setup.
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mduell
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Oct 30, 2008, 06:30 PM
 
Copying/syncing is a much better idea than RAID1 for a situation like this. RAID1 is for availability, which isn't what you're after.
     
turtle777
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Oct 30, 2008, 10:45 PM
 
Really, Time Machine is your friend.

Make the two 500GB ONE big drive, and leave your data scattered. You can back up stuff from multiple external drives to TM.

-t
     
NDBounce  (op)
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Oct 30, 2008, 11:45 PM
 
Turtle777, Can you elaborate on this a little, I am confused. If you read my OP I currently do not have any 500GB drives. I have a 320, and 2 80GB drives. Are you suggesting I should buy 2 500 drives, make one big drive and then use that for TM?

Wouldn't I be better off buying one 1TB drive rather than two new drives if I am going to make a single drive out of them? I think I must be missing something. BTW for reference the 20 80GB drives are IDE interface (I can remove the 80's and upgrade) and the 320 is SATA. Given that I do want to have all the media on one drive (so I can easily transport it if I want to bring it to a relatives, etc) what solution would you now recommend?

Thank you

O
B unce!
     
turtle777
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Oct 30, 2008, 11:51 PM
 
I know that you don't have em (yet), but you are thinking about buying some, right ?

I'd recommend to buy the biggest drive you can afford, and use it as a Time Machine backup drive.
It also would work as a transportable solution, since you can always access the complete latest backup on the TM volume directly.

-t
     
Peter
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Nov 3, 2008, 11:10 AM
 
I'm fairly sure you can't raid external drives in disk utility.
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Spheric Harlot
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Nov 3, 2008, 03:37 PM
 
Originally Posted by Peter View Post
I'm fairly sure you can't raid external drives in disk utility.
Well whatever is working the magic on my (mirror-RAID Firewire) project archive is violating a bunch of nature's laws, then.
     
Andrew Stephens
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Nov 16, 2008, 06:22 PM
 
RAIDing external drives from Disk Utility is easy. I have two 500GB FW drives doing just this quite happily for nearly a year now. They aren't backup they are for redundancy in case of an emergency. works 100% so far.
     
graxspoo
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Nov 22, 2008, 03:31 PM
 
Passing on an experience I just lived through: I had a 1TB RAID-1 array that I was using for audio work. Out of the blue I got an "Invalid Sibling Link" error, and the very important project that I had been working on disappeared off the disk. No trace. Both drives in the array were corrupt.

Luckily I was able to get most of my data back using DiskWarrior... But, I should never have had to go through this.
Consulting with the drive manufacturer, it turns out that they do NOT recommend using external drives for RAID. The reason is that there can be different latencies experienced by the disk drivers when interacting with disks, due to bus (Firewire in the case) traffic. One driver might need to retry, while the other one has already completed its write. So, things can get slightly out of sync, and then, you're just a step away from the volume directories becoming corrupt. He said the software RAID built-in to OS X is only good for internal drives, where bus latency isn't really an issue.

I don't know if his explanation is quite right technically, but I do know that my RAID array became corrupt, and this more or less never happens to me with individual drives (especially now that we have journaling). So, I am moving away from using RAID with external drives, and will be switching everything over to paired drives where one is the backup, and is periodically cloned using Carbon Copy Cloner.

Hope this helps some avoid my mistake.
     
Simon
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Nov 22, 2008, 04:40 PM
 
Originally Posted by NDBounce View Post
I am hoping to put all my media (~400GB movies/music, etc) on to one media drive. My fear, of course is that Hard Drives die. I am trying to determine the best solution to do this.
Get two drives. For example a 500 GB and a 1TB. Use the 500GB drive for your media, files, etc. Set up the other as a TM backup.

If the 500GB drive dies, your TM backup will have a copy no older than one hour. Plus you have a version history of your stuff. If your TM backup dies, you still have your primary. Get a new disk to replace the busted TM disk and you're good to go.

If you really want to go nuts on local redundancy you should get two drives for your TM backup and put them in a RAID1 (mirror). Such a RAID1 with two external drives can easily be done with Disk Utility. BTW, what Disk Utility does is soft-RAID.

I believe a RAID1 for your TM disk makes more sense than having just a RAID1 and no TM (availability, but no backup and no version history).
     
Spheric Harlot
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Nov 23, 2008, 03:30 PM
 
Originally Posted by graxspoo View Post
Passing on an experience I just lived through: I had a 1TB RAID-1 array that I was using for audio work. Out of the blue I got an "Invalid Sibling Link" error, and the very important project that I had been working on disappeared off the disk. No trace. Both drives in the array were corrupt.

Luckily I was able to get most of my data back using DiskWarrior... But, I should never have had to go through this.
Consulting with the drive manufacturer, it turns out that they do NOT recommend using external drives for RAID. The reason is that there can be different latencies experienced by the disk drivers when interacting with disks, due to bus (Firewire in the case) traffic. One driver might need to retry, while the other one has already completed its write. So, things can get slightly out of sync, and then, you're just a step away from the volume directories becoming corrupt. He said the software RAID built-in to OS X is only good for internal drives, where bus latency isn't really an issue.

I don't know if his explanation is quite right technically, but I do know that my RAID array became corrupt, and this more or less never happens to me with individual drives (especially now that we have journaling). So, I am moving away from using RAID with external drives, and will be switching everything over to paired drives where one is the backup, and is periodically cloned using Carbon Copy Cloner.

Hope this helps some avoid my mistake.
I'm unlatching my RAID this very evening.

Thanks much for the heads-up!
     
chichow
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Dec 5, 2008, 11:40 AM
 
Simon,

I've put in a Synology CS407 in. Its got 3TB RAID 5.

Can I TM to this over the network? I am not sure about TM and network...

And if I have other USB drives, what can I do to auto-schedule a backup of the Synology to take off-site?
     
Simon
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Dec 6, 2008, 04:53 AM
 
AFAIL you can do a TM backup of a mounted network volume.

You can also use a TC to do a TM backup from any client (or several clients) in your network.
     
Spheric Harlot
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Dec 6, 2008, 06:27 AM
 
Time Machine does NOT back up mounted network volumes.
     
Simon
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Dec 6, 2008, 07:04 AM
 
Originally Posted by Spheric Harlot View Post
Time Machine does NOT back up mounted network volumes.
Really? I thought you could symlink to it from your main partition and TM would follow.
     
Spheric Harlot
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Dec 6, 2008, 07:29 AM
 
That's not the same thing as just mounting it, at all.

I haven't tried symlinking, but I do know that a simple alias to a network volume is NOT followed by Time Machine.
     
Simon
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Dec 6, 2008, 09:54 AM
 
Good to know! Thanks.
     
   
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