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Re: How to track down abysmal performance ata - raid1 - crypto - vg/lv -

To: Dominik Brodowski <linux@xxxxxxxxxxxxxxxxxxxx>, Christoph Hellwig <hch@xxxxxxxxxxxxx>, linux-raid@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx
Subject: Re: How to track down abysmal performance ata - raid1 - crypto - vg/lv - xfs
From: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Date: Wed, 4 Aug 2010 05:21:22 -0400
In-reply-to: <20100804091317.GA27779@xxxxxxxxxxxxxxxxxx>
References: <20100804073546.GA7494@xxxxxxxxxxxxxxxxxxxxxxxxxx> <20100804085039.GA11671@xxxxxxxxxxxxx> <20100804091317.GA27779@xxxxxxxxxxxxxxxxxx>
User-agent: Mutt/1.5.20 (2009-08-17)
On Wed, Aug 04, 2010 at 11:13:17AM +0200, Dominik Brodowski wrote:
> > show these problems?
> 
> No, 2.6.31 to 2.6.34 show similar behaviour.

Ok, so it's been around for a while.  Can you test the write speed of
each individual device layer by doing a large read from it, using:

        dd if=<device> of=/dev/null bs=8k iflag=direct

where device starts with the /dev/sda* device, and goes up to the MD
device, the dm-crypt device and the LV.  And yes, it's safe to read
from the device while it's otherwise mounted/used.

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