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Joe Chang

40 Gigabit Ethernet

A couple of months ago, I got a pair of Intel XL710QDA2 Ethernet Converged Network Adapters, basically the fancy way of saying 40 Gigabit Ethernet that does other stuff too. I also bought the Intel QSFP+ Twin-axial cable. At that point in time, I might like to have opted for the newer Intel Omni-Path 100Gbps (56Gbps on PCI-E x4) which came out in Q4 2015 over the XL710 which came out in Q3 2104. But Intel Omni-Path only supports Linux at this time with a heavy emphasis in HPC applications, so it is unclear as to whether they will support Windows in the future. Another option was Infini-band, which other people have written about in conjunction with SMB 3.0 in Windows Server 2012.

The XL710QDA2 (dual-port) adapters were $500 each, and the cable $130. The single port XL710QDA1 was $420, so I thought having the second port was worth an extra $80 even though I am not using it yet. A 40GbE switch seems to cost about $500 per port, which I think is reasonable. There is the Cisco Nexus 9332PQ for $17K. I thought there was another vendor, Edge-Core? with a 20-port, but it is difficult searching on 40 GbE because of all the junk results. In any case, I do not believe that there is a small-office (8-12-port) 40 gigabit Ethernet switch. So, my current usage is connecting two systems directly with the QSFP+ twin-axial cable, and using the embedded 1GbE for internet connectivity.

The more readily apparent reason for high-speed networks in a SQL Server environment is to move backups from one machine to another. For my perfunctory dig at storage system vendors, the SAN vendor will say: our million-dollar product has software so you don’t need to move large backups over the network.

A less obvious reason is to achieve low latency in support of serialize high-volume calls. Transaction processing might not need high network data rates, and can probably generate high call volume on 1 GbE from multiple concurrent connections. However, there could be situations that require the highest possible call volume on a single thread and connection. Of course, in this case, the first course of action is to employ a back-to-back connection, bypassing any switches whatsoever. And definitely not have more than one switch in the path from application to database if a direct connection is not possible.

Potentially, we might think that high volume ETL could benefit from high data rate networks, but I believe that SQL Server single thread write operations are more limiting than 1 gigabit Ethernet. But perhaps more recent versions of SSIS might have better tools for parallelism.

Trying out the Intel 40GbE adapater
Back in August, when I got the XL710QDA, my test systems were running Windows Server 2016 TP5, for which Intel had beta driver. The adapter was recognized by the operating system and the beta driver installed with no issues. The Intel documentation on firmware updates was very complicated, so I did not apply any. In this setup, even though the driver installed, I could not ping across the 40GbE network. Intel support was of the opinion that the back-to-back connection should work. No diagnostic tools were provided for examining the software stack for the XL710.

Then in early October, there was a substantial hotfix for Windows Server 2016 TP5, after which SQL Server connections were going over the 40GbE. A ping test worked one way but not the other. In any case, Windows Server 2016 RTM was out about this time, so I installed both machines to RTM, applied OS hotfixes, and updated to the release driver. Now everything seems to work.

In bulk copies, network transfer rate was high and serialize network calls were also faster than on the 1GbE network (which was via a switch, not back to back). When I get a chance, I will look at how much round-trip latency reduction I would have gotten on 1GbE with a direct back to back cable. I did this about 15 years ago when Gigabit adapters came down to $300 but switches were still very expensive. If anyone is interested, I investigated on whether there was a cross-over cable for gigabit, Gigabit Ethernet Direct Connect , i.e. no special cross-over cable needed.

10 gigabit Ethernet
For people not ready to jump directly to 40 Gigabit Ethernet, then consider 10 Gigabit. Adapters are now in the $300-400 range, and switched are in the $100 per port territory. The main consideration is which interface to standardize on. Two options for short distances are 10GBase-T and SFP+ Direct-Attach. It appears CX4 is not getting traction? One might be tempted to default to twisted pair, CAT6a or CAT7 for 10GBase-T. Cables for CAT6a and 7 are really cheap, $3-10 for short length pre-made CAT6a and $7-17 for CAT7, while SFP+ cables are $50-100.

However, various sources mention that 10GBase-T latency is higher than for the other options. And in certain situations, serialize network calls for example, latency is the primary criterion. In large file transfers, latency is not as important.

Netgear actually offers small office 10 Gigabit Ethernet switches. The XS7xx models are 8, 12, 16, and 24 10GBase-T ports, with some models having additional SFP+ uplink ports. The M4300 models include one with 8 10GBase-T + 8 SFP+ and 12+12. I did not see any that were all or mostly SFP+, but the X+X should be acceptable. It is possible to use the Intel XL710 with a QSFP to 4-port SFP breakout cable.

Is the Intel 40GbE a dead-end? Intel is going their own way at 100Gbps with Omni-Fabric, which currently does not support Windows.

Mellanox has a new 100GbE that also does NVMe over fabric?

Mellanox is offering a rebase for one-purchase of their 40/100GbE switches, the SN2100 16-port? Price might be $6600-7200? with 50% rebate. This puts it at $200+ per port at the rebate rate, and perhaps $450 per port normally?

Published Monday, October 24, 2016 7:37 PM by jchang

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RichB said:

Have you looked at combining these with the 2016 storage spaces direct and local pcie flash drives (or similar) to achieve shared nothing sql clusters?

I have a feeling that might be quite an interesting combination if it works.

October 24, 2016 9:55 PM

jchang said:

I don't have the infrastructure to test storage spaces. There was a session at PASS by Brian Walters of SanDisk on storage spaces. They cited 24 and 40GB/s! They used 100GbE, not sure whose adapter, but 40GB/s must be 4 x 100GbE at linear scaling. Note iSCSI and FCOE did not scale past 2 x 10GbE back a few years. Their backend had SATA or SAS SSDs on multiple RAID controllers.

Ok, the SanDisk slide deck referenced a configuration with Mellanox 100GbE adapters and switches.

October 30, 2016 5:41 PM

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About jchang

Reverse engineering the SQL Server Cost Based Optimizer (Query Optimizer), NUMA System Architecture, performance tools developer - SQL ExecStats, mucking with the data distribution statistics histogram - decoding STATS_STREAM, Parallel Execution plans, microprocessors, SSD, HDD, SAN, storage performance, performance modeling and prediction, database architecture, SQL Server engine

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