Re: striping and mirroring with only two disks

[Nathan Lewis <nathapl@cs.okstate.edu>]

Even if it were possible, your write performance would be TERRIBLE (imaging 
writing the chunks in order - 0, 1, 2, 3....  Your disk heads would be 
thrashing constantly).  The RAID1 code already does read-balancing.  Not 
the same thing as striping, but certainly increases performance on reads, 
especially when more than one read is being done at a time.

If you wanted to try it, I think you might be able to accomplish it with 
partitions.  Partition your two disks in half, so you have:
disk1 a & b
disk2 a & b

Then mirror disk1a with disk2b (say as /dev/md0), and likewise mirror 
disk1b with disk2a (say as /dev/md1).  Then create a RAID0 array (/dev/md2) 
from those two mirrors (md0 and md1).

You could also do it the other way:
create two raid0 arrays (disk1a+disk2a=/dev/md0) (disk1b+disk2b=/dev/md1) 
then mirror them as /dev/md2.


At 01:53 PM 1/31/2004, Keld Jørn Simonsen wrote:
> Hi!
>
> Is it possible to both do striping and mirroring if you only have 2 disks?
>
> I was thinking of having the chunks organized on each disk so
> that striping reads and writes could be done. Eg. by having
>
> disk1: chunk0 chunk2 chunk4 ......   chunk1 chunk3 chunk5
> disk2: chunk1 chunk3 chunk5 ......   chunk0 chunk2 chunk4
>
> Would such a layout of chunks allow for striped reading and writing?
>
> Best regards
> keld
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