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From: malahal@us.ibm.com
To: linux-lvm@redhat.com
Subject: Re: [linux-lvm] tps for block device vs lvm device
Date: Fri, 8 Aug 2008 09:29:32 -0700	[thread overview]
Message-ID: <20080808162932.GA12253@us.ibm.com> (raw)
In-Reply-To: <f9d530070808071804s36f55963y504cdf0ccd73f00b@mail.gmail.com>

I believe, that is due to bio vs request. LVM/DM block devices receive
and use bio requests where as sdX uses requests (which are coalesced
from these bio's using elevator algorithms). So the actual disk
transactions would be fewer.

--Malahal.

unlisted [unlisted@gmail.com] wrote:
>    Why would I see 50x the amount of transactions on the lvm volume vs the
>    actual underlying block device ?
> 
>    avg-cpu:  %user   %nice %system %iowait  %steal   %idle
>               0.00    0.00   11.41   57.07    0.00   31.51
>    Device:            tps    MB_read/s    MB_wrtn/s    MB_read    MB_wrtn
>    sda             211.33         0.00        56.12          0        113
>    sdb             268.47        63.05         0.00        128          0
>    dm-0          14365.52         0.00        56.11          0        113
>    dm-1              0.00         0.00         0.00          0          0
>    sdc               0.00         0.00         0.00          0          0
>    211 tps versus 14365 tps.  The box is idle and the following command was
>    running:
> 
>    dd if=/dev/sdb of=/home/xxxxxxx/bigrandomfile.txt bs=4k count=10000000
>    Sam

> _______________________________________________
> linux-lvm mailing list
> linux-lvm@redhat.com
> https://www.redhat.com/mailman/listinfo/linux-lvm
> read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/

      reply	other threads:[~2008-08-08 16:29 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-08-08  1:04 [linux-lvm] tps for block device vs lvm device unlisted
2008-08-08 16:29 ` malahal [this message]

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