[lustre-discuss] Bandwidth bottleneck at socket?

[Patrick Farrell]

Brian,


I'm not sure what you mean by "socket level".


A starter question:
How fast are your OSTs?  Are you sure the limit isn't the OST?  (Easy way to test - Multiple files on that OST from multiple clients, see how that performs)

(lfs setstripe -i [index] to set the OST for a singly striped file)


In general, you can get ~1.3-1.8 GB/s from one process to one file with a recent-ish Xeon, if your OSTs and network can handle it.  There are a number of other factors that can get involved in limiting your bandwidth with multiple threads.


It sounds like you're always (in the numbers you report) using one client at a time.  Is that correct?


I suspect that you're limited in bandwidth to a specific OST, either by the OST or by the client settings.  What's your bandwidth limit from one client to multiple files on the same OST?  Is it that same 1.5 GB/s?


If so (or even if it's close), you may need to increase your clients RPC size (max_pages_per_rpc in /proc/fs/lustre/osc/[OST]/), or max_rpcs_in_flight (same place).  Note if you increase those you need to increase max_dirty_mb (again, same place).  The manual describes the relationship.


Also - What version of Lustre are you running?  Client & server.


- Patrick

________________________________
From: lustre-discuss <lustre-discuss-bounces at lists.lustre.org> on behalf of Brian Andrus <toomuchit at gmail.com>
Sent: Wednesday, August 30, 2017 11:16:08 AM
To: lustre-discuss at lists.lustre.org
Subject: [lustre-discuss] Bandwidth bottleneck at socket?

All,

I've been doing some various performance tests on a small lustre
filesystem and there seems to be a consistent bottleneck of ~700MB/s per
socket involved.

We have 6 servers with 2 Intel E5-2695 chips in each.

3 servers are clients, 1 is MGS and 2 are OSSes with 1 OST each.
Everything is connected with 40Gb Ethernet.

When I write to a single stripe, the best throughput I see is about
1.5GB/s. That doubles if I write to a file that has 2 stripes.

If I do a parallel copy (using mpiio) I can get 1.5GB/s from a single
machine, whether I use 28 cores or 2 cores. If I only use 1, it goes
down to ~700MB/s

Is there a bandwidth bottleneck that can occur at the socket level for a
system? This really seems like it.


Brian Andrus

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