Ken's point about performance on GCS->GCP transfers is a good one, but
John's transfer in this case must be using UDT, as that is the only
method possible for GCP->GCP transfers.
Dave's suggestion of the possible NAT traversal hit is definitely a
possibility. Another possibility with that same idea in mind is that
the connection is being negotiated on a slower route than expected. The
UDT connection is formed using ICE negotiation, which, in very simple
terms, tries to connect between every combination of interfaces on both
ends. The first one to complete the connection wins, even if that may
not be the primary interface. John mentions this is on a cluster, so
multiple interfaces that could establish a connection wouldn't be
If sticking with GCP, there isn't much you can do as far as tuning the
UDT connection. You'll want to investigate the above speculation during
a transfer, to see if the expected interface is being used. One option
is, with a subscription, increasing the concurrency via the network-use*
settings of both GCP endpoints. This should help if the resources
aren't already maxed out. Feel free to follow up with
if you need assistance with this.
I'll also echo what others have said about installing GCS if practical.
That will provide the most flexibility and tunability, and also raises
the possibility of using multiple nodes of the clusters.
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