I’m very appreciative for each person who’s provided some feedback, especially the lengthy replies.
Sounds like RoCE capable Ethernet backbone may be the default way to go *unless* the end users have some specific requirements that might need IB. At this point, we wouldn’t be interested in anything slower than 200Gbps. So perhaps Eth and IB are equivalent in terms of latency and RDMA capabilities, except one is an open standard. Thanks, Daniel Healy On Mon, Feb 26, 2024 at 3:40 AM Cutts, Tim <tim.cu...@astrazeneca.com> wrote: > My view is that it depends entirely on the workload, and the systems with > which your compute needs to interact. A few things I’ve experienced before. > > > > 1. Modern ethernet networks have pretty good latency these days, and > so MPI codes can run over them. Whether IB is worth the money is a > cost/benefit calculation for the codes you want to run. The ethernet > network we put in at Sanger in 2016 or so we measured as having similar > latency, in practice, as FDR infiniband, if I remember correctly. So it > wasn’t as good as state-of-the-art IB at the time, but not bad. Certainly > good enough for our purposes, and we gained a lot of flexibility through > software-defined networking, important if you have workloads which require > better security boundaries than just a big shared network. > 2. If your workload is predominantly single node, embarrassingly > parallel, you might do better to go with ethernet and invest the saved > money in more compute nodes. > 3. If you only have ethernet, your cluster will be simpler, and > require less specialised expertise to run > 4. If your parallel filesystem is Lustre, IB seems to be the more > well-worn path than ethernet. We encountered a few Lustre bugs early on > because of that. > 5. On the other hand, if you need to talk to Weka, ethernet is the > well-worn path. Weka’s IB implementation requires the dedication of some > cores on every client node, so you lose some compute capacity, which you > don’t need to do if you’re using ethernet. > > > > So, as any lawyer would say “it depends”. Most of my career has been in > genomics, where IB definitely wasn’t necessary. Now that I’m in pharma, > there’s more MPI code, so there’s more of a case for it. > > > > Ultimately, I think you need to run the real benchmarks with real code, > and as Jason says, work out whether the additional complexity and cost of > the IB network is worth it for your particular workload. I don’t think the > mantra “It’s HPC so it has to be Infiniband” is a given. > > > > Tim > > > > -- > > *Tim Cutts* > > Scientific Computing Platform Lead > > AstraZeneca > > > > Find out more about R&D IT Data, Analytics & AI and how we can support you > by visiting our Service Catalogue > <https://azcollaboration.sharepoint.com/sites/CMU993> | > > > > > > *From: *Jason Simms via slurm-users <slurm-users@lists.schedmd.com> > *Date: *Monday, 26 February 2024 at 01:13 > *To: *Dan Healy <daniel.t.he...@gmail.com> > *Cc: *slurm-users@lists.schedmd.com <slurm-users@lists.schedmd.com> > *Subject: *[slurm-users] Re: Question about IB and Ethernet networks > > Hello Daniel, > > > > In my experience, if you have a high-speed interconnect such as IB, you > would do IPoIB. You would likely still have a "regular" Ethernet connection > for management purposes, and yes that means both an IB switch and an > Ethernet switch, but that switch doesn't have to be anything special. Any > "real" traffic is routed over IB, everything is mounted via IB, etc. That's > how the last two clusters I've worked with have been configured, and the > next one will be the same (but will use Omnipath rather than IB). We > likewise use BeeGFS. > > > > These next comments are perhaps more likely to encounter differences of > opinion, but I would say that sufficiently fast Ethernet is often "good > enough" for most workloads (e.g., MPI). I'd wager that for all but the most > demanding of workloads, it's entirely acceptable. You'll also save a bit of > money, of course. HOWEVER, I do think there is, shall we say, an > expectation from many researchers that any cluster worth its salt will have > some kind of fast interconnect, even if at the scale of most on-prem work, > you might be hard-pressed in real-world conditions to notice much of a > difference. If you're running jobs that take weeks and hundreds of nodes, > the time (and other) savings may add up, but if we're talking the > difference between a job running on 5 nodes taking 48 hours vs. slightly > less, then?? Your mileage may vary, as they say... > > > > Warmest regards, > > Jason > > > > On Sun, Feb 25, 2024 at 3:13 PM Dan Healy via slurm-users < > slurm-users@lists.schedmd.com> wrote: > > Hi Fellow Slurm Users, > > > > This question is not slurm-specific, but it might develop into that. > > > > My question relates to understanding how *typical* HPCs are designed in > terms of networking. To start, is it typical for there to be a high speed > Ethernet *and* Infiniband networks (meaning separate switches, NICs)? I > know you can easily setup IP over IB, but is IB usually fully reserved for > MPI messages? I’m tempted to spec all new HPCs with only a high speed > (200Gbps) IB network, and use IPoIB for all slurm comms with compute nodes. > I plan on using BeeGFS for the file system with RDMA. > > > > Just looking for some feedback, please. Is this OK? Is there a better way? > If yes, please share why it’s better. > > Thanks, > > Daniel Healy > > > -- > slurm-users mailing list -- slurm-users@lists.schedmd.com > To unsubscribe send an email to slurm-users-le...@lists.schedmd.com > > > > > -- > > *Jason L. Simms, Ph.D., M.P.H.* > > Manager of Research Computing > > Swarthmore College > Information Technology Services > > (610) 328-8102 > > Schedule a meeting: https://calendly.com/jlsimms > ------------------------------ > > AstraZeneca UK Limited is a company incorporated in England and Wales with > registered number:03674842 and its registered office at 1 Francis Crick > Avenue, Cambridge > <https://www.google.com/maps/search/1+Francis+Crick+Avenue,+Cambridge?entry=gmail&source=g> > Biomedical Campus, Cambridge, CB2 0AA. > > This e-mail and its attachments are intended for the above named recipient > only and may contain confidential and privileged information. If they have > come to you in error, you must not copy or show them to anyone; instead, > please reply to this e-mail, highlighting the error to the sender and then > immediately delete the message. 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