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I'm new to raid arrays, and I'm trying to figure out what I would gain by combining this hdd:

which is a seagate cuda LP 1tb 3 gb/s

whith another seagate, but a 1tb sata3 6gb/s

From what I understand, I would get 2 tb space, but would the slower hdd significantly decrease performance in the raid?

Would this composition even benefit me?

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What's your question? Does it give more space? Is it faster? Or is it compatible? It's kinda hard to see what you're asking here – KronoS Sep 14 '11 at 14:47
I'm sorry it was unclear - it was a pretty broad question, because I was unsure of all of it really, speed, the space, the general things to be aware of when doing it with the hdds in question. but the answers I got were very informative, so I'm good :) – Dynde Sep 14 '11 at 15:04
up vote 1 down vote accepted

6 gb/s is the theoretical burst speed, which you will never see sustained, so the difference between 6gb and 3gb isn't that important. What's important is the actual sustained throughput of the drives in question.

The combination of these two in a RAID 0 will be as much as 80% faster than either drive alone, assuming that your controller is decent. If you are using the controller on your motherboard, those are "Fake RAID" controllers, which is done completely in software, in spite of what your motherboard documentation might want you to believe. You won't get the performance from a motherboard RAID setup that you would from a dedicated card.

You didn't mention what you are trying to accomplish, but for most people, the hassle and also risk of having RAID 0 isn't worth the performance benefit. RAID 0 doubles your chance of data loss, since if one drive goes bad, you lose everything on both drives.

A better configuration might be putting the Operating System on a smaller SSD drive, and using the drive you have for data, but again, that's probably not worth the trouble, unless you have some kind of ultra-high performance requirements.

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Thank you very much, I was simply curious as to whether I would gain any significant speed by striping the hdd's. I have OS on a 120gb SSD anyway. And I don't have a hw controller anyway, so I guess I can live with having the two drives seperate :) Thanks very much! – Dynde Sep 14 '11 at 14:57

Raid 0 is used for performance only: there's no protection against data loss. Imagine that instead of saving a whole file of 100MB in one disk, you'll be saving 50MB in each disk simultaneously.

For example, in a rough approximation, assuming that one HDD is really twice as fast as the other: it would save 50MB in the faster disk in x seconds and in would take 2x seconds in the slower one. Since it's done at the same time, the total saving time would be 2x seconds for 100 MB.

If you saved the same file just in the slower disk, you would spend 50MB -> 2x, 100MB -> 4x seconds. In the faster one, you would spend 50MB -> x, 100MB -> 2x.

So, using RAID 0 you'll use both disks at the same speed you would get if you had only the faster disk available.

Problems: this is a rough approximation. HDDs have access time, data burst rates, caches, etc., that impact this simulation. And it also assumes that your motherboard really provides you with the real RAID 0 abillity, so that your data won't be bottlenecked somewhere.

Remember that raid 0 doubles your problems in case of fail: since all your data will be split in two HDD, one of them failling means that you loose everything, as probably recovering half file won't be usefull.

Suggestion: why not put the most used files (like the OS, swap files, etc) in the faster drive and use the slower drive to save files that you don't need the better performance? Ex.: music files, videos, etc.

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