From: Alex Turner <armtuk@gmail.com>
To: Greg Smith <gsmith@gregsmith.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Bad iostat numbers
Date: Tue, 5 Dec 2006 01:21:38 -0500
Message-ID: <33c6269f0612042221x5820e98bl96f8d0dc4a87bd3f@mail.gmail.com> (raw)
In-Reply-To: <Pine.GSO.4.64.0612041946120.9323@westnet.com>
References: <PEEPKDFEHHEMKBBFPOOKKEHCDKAA.carlos.reimer@opendb.com.br>
<Pine.GSO.4.64.0612032336250.19679@westnet.com>
<33c6269f0612032317t9f0bc77n3ff791a5cd88fc80@mail.gmail.com>
<Pine.GSO.4.64.0612041946120.9323@westnet.com>
I agree, that MegaRAID is very stable, and it's very appealing from that
perspective. And two years ago I would have never even mentioned cciss
based cards on this list, because they sucked wind big time, but I believe
some people have started seeing better number from the 6i. 20MB/sec write,
when the number should be closer to 60.... thats off by a factor of 3. For
my data wharehouse application, thats a big difference, and if I can get a
better number from 7200RPM drives and a good SATA controller, I'm gonna do
that because my data isn't OLTP, and I don't care if the whole system shits
itself and I have to restore from backup one day.
My other and most important point is that I can't find any solid
recommendations for a SCSI card that can perform optimally in Linux or
*BSD. Off by a factor of 3x is pretty sad IMHO. (and yes, we know the
Adaptec cards suck worse, that doesn't bring us to a _good_ card).
Alex.
On 12/4/06, Greg Smith <gsmith@gregsmith.com> wrote:
>
> On Mon, 4 Dec 2006, Alex Turner wrote:
>
> > People recommend LSI MegaRAID controllers on here regularly, but I have
> > found that they do not work that well. I have bonnie++ numbers that
> > show the controller is not performing anywhere near the disk's
> > saturation level in a simple RAID 1 on RedHat Linux EL4 on two seperate
> > machines provided by two different hosting companies.
> > http://www.infoconinc.com/test/bonnie++.html
>
> I don't know what's going on with your www-september-06 machine, but the
> other two are giving 32-40MB/s writes and 53-68MB/s reads. For a RAID-1
> volume, these aren't awful numbers, but I agree they're not great.
>
> My results are no better. For your comparison, here's a snippet of
> bonnie++ results from one of my servers: RHEL 4, P4 3GHz, MegaRAID
> firmware 1L37, write-thru cache setup, RAID 1; I think the drives are 10K
> RPM Seagate Cheetahs. This is from the end of the drive where performance
> is the worst (I partitioned the important stuff at the beginning where
> it's fastest and don't have enough free space to run bonnie there):
>
> ------Sequential Output------ --Sequential Input- --Random-
> -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
> K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec %CP
> 20708 50 21473 9 9603 3 34419 72 55799 7 467.1 1
>
> 21Mb/s writes, 56MB/s reads. Not too different from yours (especially if
> your results were from the beginning of the disk), and certainly nothing
> special. I might be able to tune the write performance higher if I cared;
> the battery backed cache sits unused and everything is tuned for paranoia
> rather than performance. On this machine it doesn't matter.
>
> The thing is, even though it's rarely the top performing card even when
> setup perfectly, the LSI SCSI Megaraid just works. The driver is stable,
> caching behavior is well defined, it's a pleasure to administer. I'm
> never concerned that it's lying to me or doing anything to put data at
> risk. The command-line tools for Linux work perfectly, let me look at or
> control whatever I want, and it was straighforward for me to make my own
> customized monitoring script using them.
>
> > LSI MegaRAID has proved to be a bit of a disapointment. I have seen
> > better numbers from the HP SmartArray 6i, and from 3ware cards with
> > 7200RPM SATA drives.
>
> Whereas although I use 7200RPM SATA drives, I always try to keep an eye on
> them because I never really trust them. The performance list archives
> here also have plenty of comments about people having issues with the
> SmartArray controllers; search the archives for "cciss" and you'll see
> what I'm talking about.
>
> The Megaraid controller is very boring. That's why I like it. As a Linux
> distribution, RedHat has similar characteristics. If I were going for a
> performance setup, I'd dump that, too, for something sexier with a newish
> kernel. It all depends on which side of the performance/stability
> tradeoff you're aiming at.
>
> On Mon, 4 Dec 2006, Scott Marlowe wrote:
> > Does RHEL4 have the megaraid 2 driver?
>
> This is from the moderately current RHEL4 installation I had results from
> above. Redhat has probably done a kernel rev since I last updated back in
> September, haven't needed or wanted to reboot since then:
>
> megaraid cmm: 2.20.2.6 (Release Date: Mon Mar 7 00:01:03 EST 2005)
> megaraid: 2.20.4.6-rh2 (Release Date: Wed Jun 28 12:27:22 EST 2006)
>
> --
> * Greg Smith gsmith@gregsmith.com http://www.gregsmith.com Baltimore, MD
>
> ---------------------------(end of broadcast)---------------------------
> TIP 2: Don't 'kill -9' the postmaster
>
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To: pgsql-performance@postgresql.org
Cc: armtuk@gmail.com, gsmith@gregsmith.com
Subject: Re: Bad iostat numbers
In-Reply-To: <33c6269f0612042221x5820e98bl96f8d0dc4a87bd3f@mail.gmail.com>
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