[linux-lvm] why do striping and mirroring in LVM?

[lilha@legend.com.cn]

i know that lvm support striping now and LVM2 will support mirroring
directly later this year.
but i'm puzzled that why lvm do that?

i think the main Goals of LVM are
     1.Implement a very flexible virtual disk subsystem to handle disk
storage.
     2.Online allocation and relocation of storage.
     3.Online extension and reduction of storage.
And disk redundancy is the goals of  hardware. or software.RAID.

i think software.RAID+LVM is good idea,and that's enough.
why LVM focus on the striping and mirroring?
i don't think it's a good idea to do a big and full software.

there are any reasons and advantages to use striping or mirroring LVM than
software.RAID+LVM ?

i think the reason is LVM it does not matter where the disks are at all.
We can do the same with two big external storage towers, not just with two
disks.

but i think this reason is not enough, can anyone give me some support?
and how many people use striping or mirroring LVM£¬not software.RAID+LVM£¿


TIA for your help and sorry for my poor English.

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