Monoprice 3m QSFP+ DACs for $10.58

llowrey

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Feb 26, 2018
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$10.58 for a 3m QSFP+ DAC. Coded for Cisco.

3M Cisco Compatible QSFP+ to QSFP+ Copper Direct Attach Cable (DAC) - Monoprice.com

I understand that Mellanox is quite tolerant of DAC vendor coding. Any reason why these might not work between a Mellanox switch and card?

UPDATE: These do not work with Mellanox gear. The switch complains that the cable's data checksum is not correct. Further, the raw eeprom data seems wrong. No wonder Monoprice is dumping them.
 
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llowrey

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Feb 26, 2018
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Sadly, these cables do not work between my Mellanox switch and CX3. I get "Cable data is invalid (Wrong checksum)". When I read the raw data from the cable eeprom it's not even correctly formatted. I tried two and they both behave the same.
 

neggles

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Sep 2, 2017
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If you have an equivalent Mellanox cable with a correct cable ID EEPROM you could try cloning the data to see if that makes it work - still not worth the $ though when a genuine Mellanox (HP-branded) is usually $20-30 or so on eBay
 

llowrey

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Feb 26, 2018
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How can one go about cloning the eeprom data?

I'm stuck paying for the return shipping and it's a large percentage of the refund I'll get. If I can fix the eeprom data and the cables work I'll keep 'em.
 

neggles

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Sep 2, 2017
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You'd need an I2C EEPROM reader/writer, and something to connect to the contacts - so a QSFP+ slot. It's doable, but last time I looked into it it was harder than just replacing the cables :(

If you've got a dead 40GbE NIC lying around that you can salvage the QSFP+ cage off, and you know your way around a soldering iron/microcontroller, you could probably whip something up - but failing that it's probably going to be more trouble than it's worth.
 

llowrey

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Feb 26, 2018
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Thanks for the reply.

I figured as much. I ordered a few QSFP+ and SFP+ receptacles from digikey for about $10. I should have everything else I need on-hand. Should be fun.