striping of a 4 drive raid10

["Keld Jørn Simonsen" <keld@dkuug.dk>]

Hi

I have tried to make a striping raid out of my new 4 x 1 TB
SATA-2 disks. I tried raid10,f2 in several ways:

1: md0 = raid10,f2 of sda1+sdb1, md1= raid10,f2 of sdc1+sdd1, md2 = raid0
of md0+md1

2: md0 = raid0 of sda1+sdb1, md1= raid0 of sdc1+sdd1, md2 = raid01,f2
of md0+md1

3: md0 = raid10,f2 of sda1+sdb1, md1= raid10,f2 of sdc1+sdd1, chunksize of 
md0 =md1 =128 KB,  md2 = raid0 of md0+md1 chunksize = 256 KB

4: md0 = raid0 of sda1+sdb1, md1= raid0 of sdc1+sdd1, chunksize
of md0 = md1 = 128 KB, md2 = raid01,f2 of md0+md1 chunksize = 256 KB

5: md0= raid10,f4 of sda1+sdb1+sdc1+sdd1

My new disks give a transfer rate of about 80 MB/s, so I expected
to have something like 320 MB/s for the whole raid, but I did not get
more than about 180 MB/s.

I think it may be something with the layout, that in effect 
the drives should be something like:

          sda1             sdb1    sdc1      sdd1
           0                1       2         3
           4                5       6         7

And this was not really doable for the combination of raids,
because thet combinations give different block layouts.

How can it be done? Do we need a new raid type?

Best regards
keld