>>It seems like if we use at least 5HD with RAID 5, the data can be spread evenly between HD. Well, this is actually what I thought about RAID 5+0. But if we can also do it with RAID 5, then why RAID 5+0 exist ? I think I have to find out more about it, and get a clearer information.
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>RAID 5 requires at least 3 disks. My understanding is that the information is spread evenly, yes, but one hard disk is always used for redundancy. It seems that with 5 identical hard disks, the data would be spread among 4 hard disks, and the 5th. is used for redundancy (for the first bits; later the hard disks change places).
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>Perhaps RAID 5+0 is the name given by some manufacturers only, but I don't really know.
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>Hilmar.

No, it's not just a name. it is a combine RAID 5 and RAID 0. Look at this page
http://www.adaptec.com/worldwide/product/markeditorial.html?sess=no&language=English+US&cat=%2fTechnology%2fRAID&prodkey=talk_about_raid

And I was wrong also, I thought we can use RAID 5+0 with at least 5HD. Actually it needs 6HD minimum. More money to spend :-)