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Feynman · Feb 11, 2008, 06:21 PM

Could someone please give me their true thoughts and experience with the two?

For conversations sake I will be getting a 4 bay RAID and want to fill it up with four 1 TB drives.

I understand RAID 5 is more stable then RAID 0 but how much more?

By joining four 1 TB drives, how much storage would I really lose?

Any actual experience (as opposed to what a white paper would say) would be great! Thanks!

mduell · Feb 11, 2008, 11:39 PM

RAID0: Great read performance, great write performance, "full" capacity (smallest drive * number of drives), and you lose everything if a single drive fails.
RAID5: Good read performance, same write performance as a single drive, "n-1" capacity (smallest drive * [number of drives - 1]), and you can recover from a single drive failure.

RAID0 can be done in software (although I don't recommend it), while RAID5 requires a RAID card in OS X.

besson3c · Feb 11, 2008, 11:44 PM

Go with RAID 5 unless your data is just throw away data that you wouldn't care about losing. There is no data integrity in RAID 0. Do not backup important data to a RAID 0 and consider it safe.

Feynman · Feb 12, 2008, 12:29 AM

Originally Posted by besson3c

Go with RAID 5 unless your data is just throw away data that you wouldn't care about losing. There is no data integrity in RAID 0. Do not backup important data to a RAID 0 and consider it safe.

Now the two of you above are contradicting each other a little lol

Basically I am ripping all my DVDs to the drive. The heads on the drive will be minimal so it's not like I am doing crazy video editing.

Again, my question regarding RAID 5 - with four 1 TB drives, how much space would I be losing?

With my needs, is RAID 0 still not smart?

I need recommendations here! lol

besson3c · Feb 12, 2008, 01:02 AM

How are we contradicting each other? Mduell has explained how much space you will be losing.

If you can afford to lose your data and don't need any real insurance, RAID 0 will be fine.

Feynman · Feb 12, 2008, 05:24 AM

Originally Posted by besson3c

How are we contradicting each other? Mduell has explained how much space you will be losing.

If you can afford to lose your data and don't need any real insurance, RAID 0 will be fine.

But you make it sound like it's more than likely to fail at RAID 0.

And I was never explained how much space I would lose with RAID 5.

OreoCookie · 06:35 AM

Yes, mduell has in his second paragraph: you have an effective capacity of n-1 drives where n=4 in your case. RAID5 is a lot, lot more secure than RAID0 with four drives. If the probability of drive failure is p, the probability is slightly less than 4p that your RAID0 fails. The probability that a RAID5 fails is 6p^2 -- much, much, much smaller.

If we assume that the probability of hardware is (for the sake of argument) 5 %, then this is 20 % for a RAID0 versus 1.5 % for the RAID5.

Feynman · Feb 12, 2008, 11:22 AM

Originally Posted by OreoCookie

Yes, mduell has in his second paragraph: you have an effective capacity of n-1 drives where n=4 in your case. RAID5 is a lot, lot more secure than RAID0 with four drives. If the probability of drive failure is p, the probability is slightly less than 4p that your RAID0 fails. The probability that a RAID5 fails is 6p^2 -- much, much, much smaller.

If we assume that the probability of hardware is (for the sake of argument) 5 %, then this is 20 % for a RAID0 versus 1.5 % for the RAID5.

Okay, in English please? lol

besson3c · Feb 12, 2008, 11:43 AM

The capacity is the combined capacity of n-1 drives. N is the total number of drives that you have, which is 4 in your case. Therefore, you have the combined space of 3 of your drives, assuming they are all the same size (they should be). You have no hot spares, as 4 disks is the minimal standard RAID 5 configuration.

Do you understand now?

OreoCookie · Feb 12, 2008, 11:56 AM

mduell's `smallest drive * [number of drives - 1]' was pretty straight-forward, no?

besson3c · Feb 12, 2008, 12:39 PM

Originally Posted by OreoCookie

mduell's `smallest drive * [number of drives - 1]' was pretty straight-forward, no?

I thought so

cgc · Feb 12, 2008, 06:26 PM

Standard RAID levels - Wikipedia, the free encyclopedia

mduell · Feb 12, 2008, 09:12 PM

Originally Posted by besson3c

Go with RAID 5 unless your data is just throw away data that you wouldn't care about losing. There is no data integrity in RAID 0. Do not backup important data to a RAID 0 and consider it safe.

With either RAID5 of RAID0 you should have a separate copy of the data.
With the high price of RAID5 controllers, it's often cheaper to have two RAID0 arrays (or one RAID0 and one JBOD) with the same data on them then it is to have one RAID5 array with no backup.

Originally Posted by Feynman

Basically I am ripping all my DVDs to the drive. The heads on the drive will be minimal so it's not like I am doing crazy video editing.

I'd recommend the same thing I'm going to do: Buy two RAID0 arrays and keep the DVDs on both; it actually ends up being cheaper than RAID5 (due to the price of RAID5 controllers). This way you have a "real" second copy of your data instead of just parity (which usually works for recovery, but not always).