On Tue, Feb 1, 2011 at 4:01 AM, David Brown [off-list ref] wrote:

On 31/01/2011 23:52, Keld Jørn Simonsen wrote:

quoted

raid1+0 and Linux MD raid10 are similar, but significantly different
in a number of ways. Linux MD raid10 can run on only 2 drives.
Linux raid10,f2 has almost RAID0 striping performance in sequential read.
You can have an odd number of drives in raid10.
And you can have as many copies as you like in raid10,

You can make raid10,f2 functionality from raid1+0 by using partitions. For
example, to get a raid10,f2 equivalent on two drives, partition them into
equal halves.  Then make md0 a raid1 mirror of sda1 and sdb2, and md1 a
raid1 mirror of sdb1 and sda2.  Finally, make md2 a raid0 stripe set of md0
and md1.

If you have three disks, you can do that too:

md0 = raid1(sda1, sdb2)
md1 = raid1(sdb1, sdc2)
md2 = raid1(sdc1, sda2)
md3 = raid0(md0, md1, md2)

As far as I can figure out, the performance should be pretty much the same
(although wrapping everything in a single raid10,f2 is more convenient).

The performance will not be the same because. Whenever possible, md
reads from the outermost portion of the disk -- theoretically the
fastest portion of the disk (by 2 or 3 times as much as the inner
tracks) -- and in this way raid10,f2 can actually be faster than
raid0.


-- 
Jon
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