Userslly it is considered best practice to use nics from a known comparable 
vendor for example Intel dual port nics can be found on sites like Amazon or 
neerhg for a reasonable amount of $.

On November 18, 2022 8:02:43 PM EST, David Christensen 
<dpchr...@holgerdanske.com> wrote:
>On 11/18/22 05:23, hw wrote:
>> On Tue, 2022-11-15 at 16:42 -0800, David Christensen wrote:
>>> On 11/15/22 07:15, hw wrote:
>>>> On Tue, 2022-11-15 at 12:38 +0100, hw wrote:
>>>>> On Mon, 2022-11-14 at 13:21 +0100, hw wrote:
>
>>>>> Any ideas?  Backups over an 1GB link are excruciatingly slow ...
>>>>> 
>>>> 
>>>> Update: I booted a Fedora live system and the connection is also
>>>> intermittent.
>>>> So it's not a Debian issue.  It's still an issue, though ...
>>> 
>>> 
>>> What is the cable type?  Length?  Factory or home made?
>> 
>> I got a new cable today which is rated as cat 8.1.  It's only 1.5 meters 
>> long.
>> I have tried 3 different cables now, two of them about 1.5 and another 10 
>> meters
>> long.  Before I got the new cable, I tried the other port on the nic, and it
>> made no difference.
>> 
>> Even with the new cable, the connection is intermittent :(
>
>
>Different category cables have different characteristic impedance, and the 
>NIC's are designed for specific cables.  The EE buzzword is "transmission 
>line".  You want to use the cables that Intel designed for -- Category 6A or 
>Category 6, 100 meters or 55 meters maximum (respectively):
>
>https://www.intel.com/content/www/us/en/support/articles/000007404/ethernet-products.html
>
>
>I do not see a specification for minimum length; either on Intel or STFW.  
>Back in the day of 10BASE-*, I seem to recall hearing, reading, and/or 
>learning 2 meters minimum.
>
>
>So, I suggest trying a Category 6A factory patch cable at least 2 meters long.
>
>
>>> What is connected to the other end of the cable?  If it is a NIC in
>>> another server, what happens if you swap the two NIC's?
>> 
>> It's connected to a Broadcom NetXtreme II BCM57810 in another server.  The 
>> other
>> server has an identical mainboard and CPU in it, and the other port on the
>> Broadcom is connected to a client with the same card, and that connection 
>> works
>> fine.  So I'm assuming that the Broadcom card is ok.
>
>
>What OS's for the various machines?
>
>
>Do you compile your own kernels and/or NIC drivers?
>
>
>> I'm about to move the client into a new case in a couple days and then I 
>> might
>> swap the Broadcom from the client into the backup server.
>
>
>If you have another Broadcom NIC, what happens if you swap it with the Intel 
>NIC in the backup server?
>
>
>> Maybe I can reseat the heat sink on the card with new thermal paste.
>> Overheating might explain why the connection is intermittent.
>
>
>Do you have any diagnostic information that indicates the Intel NIC is 
>overheating?
>
>
>David
>

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