@BBigford said in SAN data transfer - very slow:
So the bottleneck is 1Gb/s and 50MB/s is about half of your theoretical max of around 100-120 MB/s so really, that is not too bad when you take into account the TCP Windowing overhead and latency and such. Could it go faster? Maybe. Reasonably? Not much.
Can you do a rough break down on the math of how you got the theoretical, please? So what are my options, short of waiting +48 hours, or having the data physically shipped to me?
Well 1GigE is your network bottleneck from the description, everything faster than that doesn't have a direct connection so aren't much of a factor (other than allowing the TCP Windows to mismatch causing more overhead.) So we start with 1,000 Mb/s.
1,000 / 8 = 125 MB/s (bits to bytes.)
So that is the theoretical max of the link with zero overhead. Rule of thumb is to assume that the actual max is 80% of Ethernet. That is 100MB/s.
So 100MB/s is pretty much the theoretical fastest that you could get over pure GigE without any bridging, switching or other slowing factors.
No consider that you are putting storage protocols onto that which means that you have some bottlenecks, at least from time to time, from the storage system so you likely will not be able to feed that perfectly. Then each conversion from Ethernet to whatever the WAN link is will add overhead in the form of the translation (different window sizes and other efficiency issues.) And then you have to add in the latency of the link - latency causes a throughput reduction when we are talking about a reliable protocol like TCP. This would not be the case for a streaming UDP connection so much, but you can't send storage data in an unreliable, best effort way so that doesn't matter. You are forced to wait for receipt responses.
Put this all together, and cutting your connection in half is normal.
