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Re: Limits of the 965 chipset & 3 PCI-e cards/southbridge? ~774MiB/s pea

To: linux-kernel@xxxxxxxxxxxxxxx, linux-raid@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx
Subject: Re: Limits of the 965 chipset & 3 PCI-e cards/southbridge? ~774MiB/s peak for read, ~650MiB/s peak for write?
From: Justin Piszcz <jpiszcz@xxxxxxxxxxxxxxx>
Date: Sun, 1 Jun 2008 07:26:09 -0400 (EDT)
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On Sun, 1 Jun 2008, Justin Piszcz wrote:

On Sun, 1 Jun 2008, Justin Piszcz wrote:

I have 12 enterprise-class seagate 1TiB disks on a 965 desktop board and it appears I have hit the limit, if I were able to get the maximum speed of all drives, ~70MiB/avg * 12 = 840MiB/s but it seems to stop aound 774 MiB/s (currently running badblocks on all drives)..

Small correction, they are 7200.11 Seagate Desktop Drives (ST31000340AS), not enterprise drives:



Basically it appears I am hammering the southbridge as for this board the PCI-e (x1) slots also traverse through the southbridge.

 6_SATA -> G965 ICH8
3_PCI-e -> G965 ICH8

From which has to ship that data across the DMI (2GB) link to the northbridge.

If one utilized a 12, 16 or 24 port raid card (but used SW RAID) on the x16 slot on the northbridge itself, would this barrier exist as the:
GMCH<->CPU is (8.5GB/s)..?

Also on the X38 and X48 the speed increases slightly:
http://www.intel.com/products/chipsets/X38/X38_Block_Diagram.jpg (10.6GB/s)
http://www.intel.com/products/chipsets/x48/x48_block_diagram.jpg (12.8GB/s)

If one asks why would one need such speed?

LTO-4 drives can write at 120 MiB/s each:

It is then therefore imperative one could sustain this rate to possibly multiple(!) tape drives on a single system.


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