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RAID 5 questions

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August 1, 2010 6:27:22 PM

I have five available 3.5" drive bays on a workstation I use for editing HD video. I want to make C:\ as a standalone 1TB drive (with external backups), and then take the remaining four 1.5TB drives, and put them in RAID 5. My questions:

About how fast will four drives in RAID 5 be, compared to two drives in RAID 0?

And about how fast would five drives in RAID 5 be, compared to two drives in RAID 0?

I would have to jump through some hoops to get five drives in RAID 5, but it might be worth it, depending.

Thanks.

More about : raid questions

August 1, 2010 6:41:25 PM

raid 5 will be slower because your are running a type of redundancy i believe.

if anything with the 4 drives, i would recommend doing a raid 10 set up with 2 striped and then thoes 2 mirrored.
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August 1, 2010 7:00:32 PM

RAID 1 is slower writing than a standalone drive, but typically slightly faster in reading.

RAID 5 with four drives should be quicker overall than RAID 0 with two drive, but the question is how much quicker is RAID 5 with four drives, than RAID 0 with two drives.
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a c 415 G Storage
August 2, 2010 1:44:35 AM

RAID 5 has very poor write performance compared to everything else. I'm thinking that video editing likely involves a fair bit of writing to work files and then writing out the final rendered result, and RAID-5 may well slow you down.
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August 2, 2010 1:52:09 AM

Well, I can put all four drives in RAID 0, and that would be really fast :)  But of course there is no fault tolerance in RAID 0, so that is no good.

But if performance is so bad in RAID 5, then why do they use it for servers? And how would I find out how much of a performance hit I would take if I put them to RAID 5?
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a c 415 G Storage
August 2, 2010 3:05:01 AM

RAID-5 is used in servers when a lot of storage is needed and performance isn't critical - often for general-purpose file shares. You almost never see RAID-5 used for write-intensive performance-critical applications like databases.

As far as performance goes, the following chart will give you an idea of what you're likely to see with RAID-5 using motherboard RAID. Some dedicated hardware RAID controllers can do better than this, though.

The chart comes from this ZDNet RAID performance article (click the chart to see a full-sized version of it):

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August 2, 2010 4:51:22 AM

Best answer selected by nazareneisrael.
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August 2, 2010 2:28:11 PM

a7xfire said:
raid 5 will be slower because your are running a type of redundancy i believe.

if anything with the 4 drives, i would recommend doing a raid 10 set up with 2 striped and then thoes 2 mirrored.


My apologies, A7. It appears you were right!
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August 2, 2010 2:44:03 PM

So RAID 5 can read quickly, but it writes slowly. Is that correct?

Do we know what the maximum write speed of four 7200RPM spin HDD's in RAID 5 would be? And does it get slower with the number of drives one adds? Or faster?

Depending on the maximum write speed, I may still be able to use it.
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August 2, 2010 4:01:40 PM

OK, I contacted Dell Tech Support. They said that the real issue for me is that it might take up to 36% of the CPU just to 'distribute parity' (i.e., decide what gets written where), which would be a real killer for me, because the CPU is already the bottleneck on my system.
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a b G Storage
August 2, 2010 5:08:46 PM

RAID 5 can be improved with a dedicated controller - add in RAID card. This offloads the processing & parity calculations to its own processor. They aren't horribly expensive, and probably add other useful features. Link below is a random sample, not a recommendation - first review I see mentions great speeds but a horrible interface:

http://www.newegg.com/Product/Product.aspx?Item=N82E168...
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a c 415 G Storage
August 2, 2010 5:13:00 PM

It's pretty difficult to predict what the maximum speed will be. You could look at benchmarks, but in the real world it depends on what software you're using and how you use it. The only way to really optimize your system is to actually try some different configurations and measure how quickly they can handle your workload.

With several drives available it's quite possible that you could get pretty good performance simply though careful organization of your folders. For example placing folders that contain the files you use on different drives will allow parallel operation of them. If the software supports multiple work folders then placing them on different drives will also help.
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August 2, 2010 5:13:58 PM

Thanks, but if I'm going to get into that class of spending then what I really need is a new mobo and processor. But I appreciate your input.
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August 2, 2010 5:17:11 PM

Sminlal, thanks. Dell recommended RAID 10, and it looks like my motherboard based controller will handle it, so I think I will try doing that. Four Seagate Barracuda 1.5TB's in RAID 10 yielding 3GB, backing up to Drobo with 4.06TB storage.

Thanks again for your help. I hope you are doing well.
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