On Thu May 30, 2019 at 08:30:02PM +0000, Andy Smith wrote:
> Hi Robin,
>
> On Thu, May 30, 2019 at 09:19:41PM +0100, Robin Hill wrote:
> > "fastest half" means the fastest half of the mirror - the NVMe drive, as
> > opposed to the slower SSD.
> >
> > I suspect the slowdown is because there's no optimisation for the
> > 2-drive RAID-10 case,
>
> I did wonder about this. I'd love to be able to try out 4 devices
> but unfortunately I can't afford to buy 2 SSDs and 2 NVMe at once!
>
> For testing purposes do you think it would be worth faking it with
> partitions, i.e. 2 partitions on each device making a 4 device
> RAID-10?
>
It depends on what you're trying to test. I don't think it'll work for
performance testing - I think md is smart enough to recognise that the
partitions share the same underlying disk and avoid concurrent
reads/writes. Even if not, you'll just be emphasising the performance
difference of the SSD.
Is your interest in RAID-10 for future expansion? I can't see any other
reason not to just use RAID-1 for a 2-device array of solid state
drives.
Cheers,
Robin
