SA5i+ Raid 1+0 confusion

[piken]

When setting up an array I only see a choice for
raid levels 0,1+0 and 5. This confuses me....

If I only install 2 drives and choose 1+0 does the controller see this and really only create a mirror(level 1) and when I install 4 drives and choose 1+0 does it then do mirror and stripe?

Or does it mirror & stripe even on just 2 drives,
for some reason I was thinking that 4 drives mirrored and
striped would only give the size of one drive. ie.....

2 x 36g = 72g level 0
2 x 36g = 36g level 1 (mirrored)
4 x 36g = 36g level 1+0 (mirrored & striped)

But of coarse my thinking must be wrong, because
4 x 36g = 72g when I configured it for 1+0

Does not striping use any space?

Any comments...........

 

[technome]

With two drives you cannot mirror and stripe, it is one or the other. Two drives striped, is raid 0, two drives mirrored is raid 1. Stay far away from raid 0, only suitable for temporary files, never for the OS or data.

To have a volume mirrored and striped , requires a minimum of 4 drives.

Raid 1+0, will create a 72 gig volume, faster than a raid 1 array. Striping refers to extending the space which can be used in a volume with combination of two or more drives. It is the mirroring part which creates a space loss. Raid 10, as with raid 5, increases in throughput as drives are added past the minimum number. A raid 10 with 10 drives, 5 per drive channel with give excellent performance.

If you have a two channel raid controller, place the drives as evenly as possible on both channels, as this increases raid throughput.

 

[piken]

Thanks for your reply.

I understand the striping better now, but that's why
I got so confused, in setting up the raid array under compaq
it only has 0,1+0,5 wether you put 2 drives or four drives
in your array. In other words even if you use only 2 drives
your choices are 0,1+0. I was thinking your choices should
be 0,1 with 2 drives . I think it sees you only have 2 drives an defaults to 1 if you choose 1+0 and only stripes and mirrors if you install 4 or more drives.