Raid 0 with external hard drives?

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Level 3

649 points

Raid 0 with external hard drives?

hi,
I'm currently thinking about getting an iMac, but since I want to back up my data with time machine I have the following question:
I was wondering if it would be possible to merge two external hard drives into one via RAID 0 (I believe Mac OS X has a RAID-Tool on board?) and use that merged hard drive as a time machine backup drive?

otherwise I would have to get one large external drive, which I'd rather avoid if possible.

thanks for answers 🙂

Macbook, Mac OS X (10.6.2), 13'' Late 2008

Posted on Mar 12, 2010 10:03 AM

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Answer 1

kmac1036

Level 4

2,370 points

Mar 15, 2010 6:33 AM in response to nachdenki

thanks for the additional info. here are my thoughts:

1. 2TB time machine drive unnecessary for a macbook, especially if you only have a 250gb or 500gb drive even, 1Tb is plenty. you can partition the other drive so it matches the partition size of yor macbook & then use carbon copy cloner or super duper to generate a live clone (set this up so it deletes removed files, don't keep the older version, TM is already doing this for you), which is bootable in emergencies. you have the leftover space to use for other things.

2. I speak from experience on setting up the RAID. doing a stripe with 2 external drives is a royal pain in the arse. it was bad enough in a tower trying to do RAID 1. I gave up & went with RAID 1 cases from OWC.

3. If you insist on having 2TB, then do a SPAN.

I setup my MBP like I mentioned in #1. 24 hours after I did, my OS X partition - with all of my stuff - got nuked due to a mishap with bootcamp (was trying to delete the win partition which failed terribly). booted up holding option & selected my carbon copy drive. recovered some file from time machine & imaged the drive back over to the laptop later in the day when I had time.

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Answer 2

Kappy

Level 10

361,741 points

Mar 12, 2010 10:33 AM in response to nachdenki

Yes, you can do that as long as both drives remain connected and turned on. Disk Utility contains the RAID options. Use Disk Utility Help from the Help menu and search for "raid" to get help articles on how to configure a RAID array. The DU software supports RAID 0 (striped) and RAID 1 (mirrored.) I presume you want the striped RAID.

Ideally both hard drives in the externals should be identical as should the enclosures, the bridge board chip, and the type of connection (FW or USB.) If any of these are not identical then it will affect the array's performance.

A TM backup drive should be at least twice the capacity of the drive it backs up to avoid future disk full problems.

Note that in a striped RAID array if one drive goes bad then all the data stored on the array will be lost.

Creating a RAID array erases all the drives used in the array.

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Answer 3

kmac1036

Level 4

2,370 points

Mar 12, 2010 10:33 AM in response to nachdenki

yes, disk utility app will do this for you in OS X...

but I strongly advise against it, especially with USB or firewire. also, RAID 0 is considered "scary raid" as if one drive fails or falls out of the array, you lose ALL data. RAID 0 takes your data & splits it in half between the drives. now spanning or SPAN adds the drives together as one big disk. once one fills up, it then starts automatically storing on the 2nd drive.

if you want RAID 0, then get an external case that supports it with 2 drives already installed. span works with any number of drives, but if one falls out, then you may have the same issues as with RAID 0. The reason RAID 0 is so picky is that it's for performance only, short term storage. Identical drives installed internally (either a case or inside a computer) is the only correct way to do this.

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Answer 4

nachdenki Author

Level 3

649 points

Mar 14, 2010 4:31 AM in response to nachdenki

thanks for the answers.
I'm not really that afraid of data loss in this case. in case one of my drives fails, all data is lost, true, but I actually only need it for time machine and, for that matter, I only need the latest time machine backup since I only need it in case my internal hard drive fails. So if one of my external drives fails, I can just replace it. My backups will be lost, but since I only need a single (latest) backup, I can just create a new one after I replaced the hard drive, can't it?

Only REAL issue would be if my internal and external drive fail at the same time, which seems kinda unlikely, doesn't it?

thanks for all your help though!

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Answer 5

Mar 14, 2010 6:40 AM in response to nachdenki

Hi nachdenki;

You can do whatever you want but I tend to agree with the other posters that RAID0 is not the proper solution for you. It will only give you additional problems and no benefits.

Allan

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Answer 6

The hatter

Level 9

60,990 points

Mar 14, 2010 6:45 AM in response to nachdenki

I just picked up a 1.5TB drive for $109. Throw in the cost of case.

If I had only one, it would be a cloned image of my hard drive with SuperDuper, and then add TimeMachine (and update the clone image 'as need' before updates or when I have something new).

Never rely on just one backup set. Laptop hard drives have shorter life, drives can fail, or power goes out while the backup or restore is running... always have one backup that is in reserve and off line.

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Answer 7

nachdenki Author

Level 3

649 points

Mar 14, 2010 12:03 PM in response to nachdenki

well, if you all say that RAID0 isn't the way to go I will probably listen to that, but I was wondering: Isn't a hardware failure with a single external drive just as likely as with two external drives connected via RAID0? I mean, sure, when you have a RAID0 it will be useless as soon as ONE of the two drives fail, but considering that I can replace a hard drive in case it fails and considering that hard drive failures don't occur all the time, shouldn't a RAID0 be sufficient (In my entire life I experienced a single hard drive failure, but maybe I just got lucky).

It's just that if I use a RAID0, I could use hard drives I already own (which are currently used in my PC), if I don't I have to buy a 2TB hard drive (and, honestly, the iMac is pretty expensive as it is, so I'd rather avoid additional costs)

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Answer 8

Kappy

Level 10

361,741 points

Mar 14, 2010 12:24 PM in response to nachdenki

Technically there isn't a difference if a drive fails, but if your data are recoverable, then you can recover it from a single drive backup. But in a RAID0 array that won't be possible when one drive fails because no data can be recovered from the functioning drive or the failed drive. So there is a greater risk of data loss with a RAID0.

A better solution to protect against drive failure is a RAID1 - mirrored. Two 1 TB drives in a mirrored RAID provides 1 TB of space. If one drive fails all your data are intact on the other drive. This is the configuration I use for backup on my Mac Pro.

I've rarely had a drive fail but in a research paper done by Google based on their server farm nearly 30% of the drives failed within one year of service.

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Answer 9

Mar 14, 2010 12:30 PM in response to nachdenki

Hi nachdenki;

No. If you have n drive in RAID0 then you increase your chances for data lost by a factor of n times hence a RAID0 array with two drive has twice the chances of data lost or at lest that is what I was told since 1981 in IT support.

Plus on top of that increased risk there are also more problems with RAID arrays then just plain disks to content with also.

Allan

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Answer 10

Mar 14, 2010 1:01 PM in response to nachdenki

RAID0 is pointless with modern HD's over a FW800 connection. You won't have enough bandwidth to see any improvements. Your limited to about 80MB/s. Recent 500GB platters can burst at 110MB/s + on a single drive. I'd RAID1 or just get 1 external drive or 2 and JBOD them. Unless you want to RAID0 some HD's from 2002:-)

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Answer 11

nachdenki Author

Level 3

649 points

Mar 14, 2010 3:39 PM in response to nachdenki

I'm starting to think I might not have made myself clear at the beginning (my english might not be that good, sorry for that ;-))
First of all, thanks for all your advice, I really appreciate it.

secondly, I think I need to make something clear: I don't plan on creating a RAID0 with my internal drive or anything like that. I just want to put two 1TB drives (both external!) together because I will have two of them to spare when I get my imac (as they are currently built into my PC) and I need at least a 2TB drive as a time machine backup drive.
So my choices are: Buying a new 2TB drive and doing nothing with my current 1TB drives or just putting the 1TB drives together in RAID0 and using them for backup.
Also, as I said before, it doesn't really matter if my RAID0 fails, as it is only my backup drive (so I still have everything I need from there on my actual iMac). So if my RAID0 fails, I just replace it with a single 2TB drive (hopefully they will be cheap by then) and let time machine create a new backup on the new drive.

Anyway, I think I see the problems with RAID0 now and when I get my imac I will certainly think about what to use as a time machine backup drive. Not sure what I will do though. But I think I go for the RAID0 until one of my 1TB drives fail and get a 2TB drive then and use that from then on.

Thanks for all your help 🙂

(BTW, @BoyHowdieDoo: I'm also not doing it for the performance improvement or anything, I don't really care about that since it's only a time machine backup drive)

Message was edited by: nachdenki

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