Re: high load, no bottleneck

[christos%zoulas.com@localhost (Christos Zoulas)]

On Sep 19, 11:35am, buhrow%nfbcal.org@localhost (Brian Buhrow) wrote:
-- Subject: Re: high load, no bottleneck

|       Hello.  the worst case scenario is when a raid set is running in
| degraded mode.  Greg sent me some notes on how to calculate the memory
| utilization in this instance.  I'll go dig them out and send them along in
| a bit.  In theory, if all your raid sets are in degraded mode at once, and
| i/o is busy, you could be highly impacted, since you can have up to 40
| i/o's outstanding for each raid set with my configuration option.  However,
| even on machines with multiple raid5 sets, with 2 of them running in
| degraded mode, I've not seen a memory bottleneck.  I don't recommend this,
| of course, but somethimes stuff happens.  In any case, except for the
| potential memory utilization, there's no down side to setting this number
| in the kernel and not worrying about it anymore.  In fact, this is what I
| do for all our machines around here regardless of whether the machine is
| hosting raid1 sets, raid5 sets or a combination of the two.

If we are going to add a sysctl, we might also put a different value for
the raid-degraded condition? Ideally I prefer if things autotuned, but that
is much more difficult.

christos