On Monday August 22, gsslist+linuxraid@xxxxxxxxxxxxxxxxxx wrote:
> Is there any advantage to RAID10 over creating an LVM volume group across
> the same number of RAID1 pairs? LVM does striping, after all. Am I
> overlooking something?
There are certainly some situations where 'raid10' and 'LVM over
raid1' provide essentially the same service, so you probably choose
whichever you are familiar with.
There are also situations where one or the other provides better
service.
Advantages of LVM over raid1:
- If you want to use LVM for general logical volume management
(growing volumes seamlessly), then it probably makes sense to use
LVM over raid1.
- The various raid1 pairs can be different sizes.
Advantages of RAID10:
- single integrated system - only one tool to use.
- One hot spare can service the whole array (though the spare-group
function of mdadm can support this in the other case too).
- A raid10 can consist of an odd number of drives (if you have a
cabinet with, say, 8 slots, you can have 1 hot spare, and 7 drives
in a raid10. You cannot do that with LVM (or raid0) over raid1).
- raid10 has a layout ('far') which theoretically can provide
sequential read throughput that scales by number of drives, rather
than number of raid1 pairs. I say 'theoretically' because I think
there are still issues with the read-balancing code that make this
hard to get in practice (though increasing the read-ahead seems to
help).
So, choose the setup which best meets your needs.
NeilBrown
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