Bjoern,
You may find that hoping for a doubling of performance by using RAID 1 is a little on the optimistic side. Except on very long sequential reads, media transfer rates are unlikely to be the limiting factor in disk throughput. Seek and rotational latencies are the cost factor in random I/O, and with RAID 1, the performance gain comes from reducing the mean latency -- on a single request, one disk will be closer to the data than the other. If the software that's handling the RAID 1 will schedule concurrent requests, you lose the advantage of reducing mean latency in this fashion, but you can get some improvement in throughput by overlapping some latency periods.
While not wanting to argue against intelligent I/O design, memory is cheap these days, and usually gives big bang-for-buck in improving response times.
As to the specifics of how one level or another of Linux implements RAID 1, I'm afraid I can't shed much light at the moment.
Regards,
Mike
On Fri, 2002-11-22 at 06:24, Bjoern Metzdorf wrote:
> A mirrored 2x36 setup will probably yield a marginal hit on writes (vs a
> single disk) and an improvement on reads due to having two drives to read
> from and will (based on the Scientific Wild Ass Guess method and knowing
slightly offtopic:
Does anyone one if linux software raid 1 supports this method (reading from
both disks, thus doubling performance)?
Regards,
Bjoern
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Michael Nielsen
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