NeilBrown wrote:
On Tue, April 21, 2009 10:44 am, John Robinson wrote:
That's more like it, and no more rattling. Can I tune settings for the
internal bitmap, or is this something which will have improved anyway
since my kernel (2.6.18-128.1.6.el5.centos.plusxen so essentially a
prominent North American Enterprise Linux vendor's EL5 codebase for
md/raid5)? I mean, I do want the bitmap, but I hadn't realised it was
quite so expensive (not that it matters much in this particular
application).
I don't think newer kernels make any different to bitmap related
performance, though there might be some general raid5 improvements since
then.
There are two tunables for bitmaps. Chuck size and delay (though the
delay doesn't seem to be in the man page).
It isn't in the man page, and
mdadm --help | egrep 'bitmap|delay'
comes up empty as well. So then I looked at the strings:
strings $(type -p mdadm) | less
and I not only found it, but found that you have a vast bunch of
duplicate strings, including some which are saying the same thing but
expressed in several ways. If I might quote my offspring, "That's ugly,
dude!"
Anyway, setting "--delay N" (sec) does exactly what you predicted, not much.
--
bill davidsen <davidsen@xxxxxxx>
CTO TMR Associates, Inc
"You are disgraced professional losers. And by the way, give us our money back."
- Representative Earl Pomeroy, Democrat of North Dakota
on the A.I.G. executives who were paid bonuses after a federal bailout.
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