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Can any 2 drives in a array of 4 drives and loose no data

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Ben Edwards
Can any 2 drives in a array of 4 drives and loose no data
on Apr 13, 2011 at 12:25:53 pm

OK, I found out something and it gave me a warm feeling inside but thought I would check here if I am correct.

I have been told that is I have a RAID 10 (striped/mirrored/parity) array of 4 drives is ANY 2 of the drives fail the I will not loose data.

If I was simply using RAID 1 for 4 drives I basically have 2 mirrored pairs so if 2 drives go in the same pair I loose data.

I guess its the parity that makes the difference. In RAID 5 parity means I get 2/3 of the storage (rather than 1/2 for mirroring). With RAID 10, if my understanding is correct, I still only get 1/2 storage but ANY2 can fail (there are no mirrored pairs as such).

In this case (for 4 drives) RAID 10 is more secure than RAID 1.

Ben

--
Ben Edwards - Freelance Filmmaker
http://www.funkytwig.com


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Bob Zelin
Re: Can any 2 drives in a array of 4 drives and loose no data
on Apr 15, 2011 at 4:58:15 am

then you only get 2 drives worth of data, with 4 drives, and they all run as slow as a single drive.
Why would you do this ?

Get a RAID 5 chassis (if you have 6 or more drives you can do a RAID 6, and have 2 drives fail).
This will give you greater performance, and you can stop the RAID 10 silliness.

Bob Zelin



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Ben Edwards
Re: Can any 2 drives in a array of 4 drives and loose no data
on Apr 15, 2011 at 10:16:26 am

My main concern is not loosing anything, drives are dirt cheap (2TB under $100).

My question was about using 4 drives, not 6. Thats what I have. It is a personal storage system for video editing.

If I go for RAID 10 I am striping so why are you saying it will be as slow as a single drive (not that that matters to me).

There seems to be a general condenses that RAID 10 very secure and performant.

I have looked at:

http://en.wikipedia.org/wiki/RAID (General)
http://www.webopedia.com/TERM/R/RAID.html (General)
http://www.tomshardware.com/reviews/RAID-SCALING-CHARTS,1635-4.html (Raid 10)
http://www.tomshardware.com/reviews/RAID-SCALING-CHARTS,1662-2.html (RAID 5)
(and many more)

You seem to be contradicting much I have read so far. Am I missing something?

Regards,
Ben

--
Ben Edwards - Freelance Filmmaker
http://www.funkytwig.com


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Alex Geroulaitis
Re: Can any 2 drives in a array of 4 drives and loose no data
on Apr 15, 2011 at 8:10:18 pm

[Ben Edwards] "I have been told that is I have a RAID 10 (striped/mirrored/parity) array of 4 drives is ANY 2 of the drives fail the I will not loose data."

Not my understanding - can you tell me where you read that?

RAID 10 is a combination of striping and mirroring - but no parity.

With any two drives failing there is a possibility of losing data - depends on which drives fail. If both drives in a mirrored set fail - all data is toast.

Alex (DV411)


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Ben Edwards
Re: Can any 2 drives in a array of 4 drives and loose no data
on Apr 19, 2011 at 11:20:23 am

I included links.

In terms of any 2 drives failing and not loosing any data I think this is incorrect (it was info from a support chat with Startech). With RAID 10 2 drives can fail and you do not always loose any data but if the 2 drives are in the same mirror I think you loose all or some.

What I had issue with was that RAID 10 is the same speed as a single drive. The 0 in raid 10 (it is in fact 1+0) is striping so it is faster. It is not as fast as raid 5 (in most cases) but it is faster than a single disc.

I ended up deciding to go for RAID 5. Although RAID 10 is a little more secure (loosing 2 or 4 does not always mean you loose data) RAID 5 does give you more storage.

One of the main factors is that you do not want to get lulled into a false seance of security. If it is really important data you should have it on another drive (preferebly off site). There is also the danger that your RAID array goes bang and takes out all the drives or that there is a fire/flood etc.

Ben

--
Ben Edwards - Freelance Filmmaker
http://www.funkytwig.com


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