Messages in this thread | | | Date | Sat, 25 Sep 2004 18:05:21 -0700 (PDT) | From | Timothy Miller <> | Subject | Re: [Fwd: Re: HIGHMEM4G config for 1GB RAM on desktop?] |
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> -------- Original Message -------- > Subject: Re: HIGHMEM4G config for 1GB RAM on desktop? > Date: Wed, 01 Sep 2004 07:52:46 +0000 > From: Miquel van Smoorenburg <miquels@cistron.nl> > To: Timothy Miller <miller@techsource.com> > CC: linux-kernel@vger.kernel.org > References: <200408021602.34320.swsnyder@insightbb.com> > <20040804120633.4dca57b3.akpm@osdl.org> > <411ABF85.2080200@techsource.com> <41336CB1.6030105@techsource.com> > <cgvpb4$ljq$1@news.cistron.nl> <4134FFC3.50409@techsource.com> > > On Wed, 01 Sep 2004 00:46:27, Timothy Miller wrote: > > Miquel van Smoorenburg wrote: > > > In article <41336CB1.6030105@techsource.com>, > > > Timothy Miller <miller@techsource.com> wrote: > > > > > >>Timothy Miller wrote: > > >> > > >>>Hey, that rings a bell. I have a 3ware 7000-2 controller with > two > > >>>WD1200JB drives in RAID1. I find that if I dd from the disk, I > get > > >>>exactly the read throughput that is the max for the drives > (47MB/sec). > > >>>However, if I do a WRITE test, the performance is miserable. > > > > > > Try setting /sys/block/sda/queue/nr_requests to twice the number > > > in /sys/block/sda/device/queue_depth > > > > This will improve write performance? > > You won't know before you try it ofcourse. It helps on my 85xx > controllers. > The problem is that the internal queue size of some 3ware controllers > (queue_depth) is larger than the I/O schedulers nr_requests so that > the I/O scheduler doesn't get much chance to properly order and merge > the requests. > > I've sent patches to 3ware a couple of times to make queue_depth > writable so that you can tune that as well, but they were refused > for no good reason AFAICS. Very unfortunate - if you have 8 JBOD > disks attached, you want to set queue_depth for each of them to > (max_controller_queue_depth / 8) to prevent one disk from starving > the other ones, but oh well. > > > And if this helps, how do I make > > it permanent? > > Can't say, depends on your distribution. For recent Debian at > least you can use /etc/sysctl.conf >
I tried the suggestions above of setting /sys/block/sda/queue/nr_requests to twice the number in /sys/block/sda/device/queue_depth.
It brought up my write performance from 12.5MB/sec to 13.2MB/sec. An improvement, but not much of one, and definately far less than the capability of the drive which I have measured to be around 36MB/sec.
(I tested each drive of my RAID1 separately on the built-in IDE controller. What I found was that the 3ware was slighly faster on reads, but WAY slower on writes, compared to the drives individually on the IDE controller.)
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