From: Luke Lonergan <llonergan@greenplum.com>
To: Steinar H. Gunderson <sgunderson@bigfoot.com>
Cc: Jeffrey W. Baker <jwbaker@acm.org>
Cc: pgsql-performance@postgresql.org
Subject: Re: Huge Data sets, simple queries
Date: Tue, 31 Jan 2006 17:35:32 -0800
Message-ID: <C0055064.1B67C%llonergan@greenplum.com> (raw)
In-Reply-To: <20060201012615.GA31927@uio.no>
Steinar,
On 1/31/06 5:26 PM, "Steinar H. Gunderson" <sgunderson@bigfoot.com> wrote:
> cassarossa:~# grep md1 /proc/mdstat
> md1 : active raid1 sdf6[1] sda6[0]
> cassarossa:~# dd if=/dev/sda6 of=/dev/null bs=8k count=400000
> [system at about 35% wait for I/O and 15% system, according to top]
> 400000+0 records in
> 400000+0 records out
> 3276800000 bytes transferred in 54,488154 seconds (60137842 bytes/sec)
> [system at about 45% wait for I/O and 7% system -- whoa?]
> 400000+0 records in
> 400000+0 records out
> 3276800000 bytes transferred in 52,523771 seconds (62386990 bytes/sec)
>
> I'm not sure if it _refutes_ the assertion that the Linux RAID-1 driver can
> do balancing of sequential reads, but it certainly doesn't present very much
> evidence in that direction. BTW, sda and sdf are on different channels of a
> dual-channel (onboard, connected via PCI-X) Adaptec board, so I doubt the bus
> is the limiting factor.
Yep - 2MB/s is noise. Run a RAID0, you should get 120MB/s.
Incidentally, before this thread took a turn to RAID10 vs. RAID5, the
question of HW RAID adapter versus SW RAID was the focus. I routinely see
numbers like 20MB/s coming from HW RAID adapters on Linux, so it's nice to
see someone post a decent number using SW RAID.
We're very happy with the 3Ware HW RAID adapters, but so far they're the
only ones (I have two Arecas but I mistakenly ordered PCI-E so I can't test
them :-(
- Luke
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To: pgsql-performance@postgresql.org
Cc: llonergan@greenplum.com, sgunderson@bigfoot.com, jwbaker@acm.org
Subject: Re: Huge Data sets, simple queries
In-Reply-To: <C0055064.1B67C%llonergan@greenplum.com>
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