priocscan vs fcfs

["Emile `iMil' Heitor" <imil%home.imil.net@localhost>]

Hi,

I've never been really happy with my NetBSD RAIDframe NAS, never really got the
speed I was supposed to even with the right alignment / raid layout etc.

Today I dug into `dkctl(8)' while searching if cache was enabled for read and
write, and I came across the "strategy" command.
Long story short, changing from priocscan to fcfs strategy multiplied my NAS's
write speed by 6! I changed the strategy for all disk members:

# dkctl wd0 strategy fcfs
# dkctl wd1 strategy fcfs
# dkctl wd2 strategy fcfs

and also for the RAIDframe:

# dkctl raid0 strategy fcfs
/dev/rraid0d: priocscan -> fcfs

as changing it only for the disk members was apparently counter-productive.
And there we go, from a 40/50MB/s write average to a stunning 200 to 300MB/s,
which is more like what the disks can theroically do.

Could anyone with some background on these strategies explain what's behind the
curtain? I couldn't really find precise documentation on this matter...

Thanks,

----------------------------------------------------------------
Emile `iMil' Heitor * <imil@{home.imil.net,NetBSD.org,gcu.info}>
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