Re: raid10: unfair disk load?

[Michael Tokarev <mjt@tls.msk.ru>]

maobo wrote:
> Hi,all
> Yes, Raid10 read balance is the shortest position time first and
> considering the sequential access condition. But its performance is
> really poor from my test than raid0.

Single-stream write performance of raid0, raid1 and raid10 should be
of similar level (with raid5 and raid6 things are different) -- in all
3 cases, it should be near the write speed of a single drive.  The
only possible problematic cases is when you've some "unlucky" hardware
which does not permit writing into two drives in parallel - in which
case raid1 and raid10 write speed should be less than to raid0 and
single drive.  But even ol'good IDE drives/controllers, even if two
disks are on the same channel, permits parallel writes.  Modern SATA
and SCSI/SAS should be no problem - hopefully, modulo (theoretically)
some very cheap lame controllers.

> I think this is the process flow raid10 influence. But RAID0 is so
> simple and performed very well!
> From this point that striping is better than mirroring! RAID10 is
> stipe+mirror. But for write condition it performed really bad than RAID0.
> Isn't it?

No it's not.  When the hardware (and drivers) is sane anyway.

Also, "speed" is a very objective thing, so to say - it very much
depends on the workload.

/mjt