thinking about this:

I don't think you get the striping performance of raid10,f2 with this
layout. And that is one of the main advantages of raid10,f2 layout.
Have you tried it out?

since you have a raid1, you don´t need striping, you can read from any
mirror, the information is the same, raid1 read is as fast as raid0
read, just write is slower (it must read on each mirror)
the only problem is raid0 part, or you use linear or stripe, i think
raid10 mdadm algorithm use stripe for raid0 part

2011/2/1 Keld Jørn Simonsen [off-list ref]:

On Tue, Feb 01, 2011 at 11:01:33AM +0100, David Brown wrote:

quoted

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.

I don't think you get the striping performance of raid10,f2 with this
layout. And that is one of the main advantages of raid10,f2 layout.
Have you tried it out?

As far as I can see the layout of blocks are not alternating between the
disks. You have one raid1 of sda1 and sdb2, there a file is allocated on
blocks sequentially on sda1 and then mirrored on sdb2, where it is also
sequentially allocated. That gives no striping.

quoted

I don't think there is any way you can get the equivalent of raid10,o2
in this way.  But then, I am not sure how much use raid10,o2 actually is
- are there any usage patterns for which it is faster than raid10,n2 or
raid10,f2?

In theory raid10,o2 should have better performance on SSD's because of
the low latency, and raid10,o2 doing multireading from each drive, which
raid0,n2 does not.

We lack some evidence from benchmarks, tho.

best regards
keld
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-- 
Roberto Spadim
Spadim Technology / SPAEmpresarial
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