RAID10 not working in install

Bill Davidsen davidsen at
Sun Feb 24 16:22:06 UTC 2008

Stuart Sears wrote:
> Brian Chadwick wrote:
>> Bill Davidsen wrote:
>> my understanding of RAID 10 is that its a mirrored array of striped
>> disks. Hence 4 disks, well at least 4 partitions, required.
> not exactly. The RAID10 target for mdadm will work on fewer disks -
> effectively it does striping and mirroring internally (think, in rough
> terms of >=2 stripes for each write, arranged such that each copy of a
> chunk is written to a different disk.)
> to the OP:
> However, I hardly see the point on only 2 disks. What will you gain from
>  this that you don't gain from RAID1? you are more-or-less just striping
> twice, once in each direction, for each write.
The raw read speed on a RAID1 array is the speed of a single drive. The 
raw read speed for RAID10(far) is N times that, N being number of 
drives. That's the same speed as RAID0, essentially. So RAID10 is 
somewhat slower for write and much faster for read. That's desirable for 
many things.

There's info in the md and mdadm man pages about the details.

Bill Davidsen <davidsen at>
   "We have more to fear from the bungling of the incompetent than from
the machinations of the wicked."  - from Slashdot

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