From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bill Davidsen Subject: Re: Poor write performance with write-intent bitmap? Date: Tue, 21 Apr 2009 12:00:23 -0400 Message-ID: <49EDED97.5010706@tmr.com> References: <49ED096E.1000002@anonymous.org.uk> <49ED16F7.3040906@anonymous.org.uk> <4081b80da35818efbc07723240f8ea36.squirrel@neil.brown.name> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <4081b80da35818efbc07723240f8ea36.squirrel@neil.brown.name> Sender: linux-raid-owner@vger.kernel.org To: NeilBrown Cc: John Robinson , Linux RAID List-Id: linux-raid.ids 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 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.