> I know nothing about MD, but i would not say that 10Mb/s is poor.
>
> As a comparison, on my single SCSI disk drive, i get 3Mb/s (the
> disks are not very new, i admit, but they are still Fast SCSI 2
> linked to a PCI controler)
>
> According to me, 5Mb/s is a resonable performance for a single
> disk, so 10Mb per seconds for 2 disks sounds fine.
they are four!
> About your test report, i was surprised to see the line:
> Ultra SCSI: Disabled
> If you want top performances, you probably need Ultra SCSI bus
> (20 Mb/S if narrow, 40 Mb if wild)
> since 2 disks require twice more bandwild on the SCSI bus that
> a single one.
the theory is: ok 1 disk <= 8 MB/s --> 2 disks could use a 16MB/s
bandwidth, well under 20 MB/s peak SCSI2-wide bandwidth.
I use TWO controllers, each one driving TWO disks, so I have a 4 disks
striping setup.
> Ok the Adaptec controler as two SCSI bus: did you verify that
> the two disks that are linked in each grap are liked to a
> different SCSI bus.
they are 2 different controller boards !! I you look at the URL I
referenced, you can see the complete setup. It would be really useful.
Anyway, looking at the md driver source code, that moderate speed-up is ok
as there is (it seems to me) no I/O overlapping between different disks
accesses. ie. when a block write operation is dispatched to a disks, it is
someway waited for completion (ok, not properly, but I tested with
250-500 MB write operations, so caching sould have no effect; moreover it
is a waste of cycles).
regards.
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