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I'm a little over 2 days deep into a 5 day .vhd upload using the Add-AzureVHD in Windows Azure Powershell and I'm perplexed to the speed (or lack thereof) of this operation. The .vhd is a 300GB file hosted on a SAN (iSCSI) and every part of this operation seems to be slower than it should be. Prior to upload, an MD5 hash is calculated and this occurred at an alarmingly slow rate taking a full 16 hours to complete. Although this is in no way acceptable to me, I"m more curious as to why my upload seems capped at 10.8 Mbps. I have a 20 Mbps upload pipe that is relatively clear according to my live monitoring at the firewall. I took a look at the Resource Monitor, specifically the TCP Connections section under the Network tab and noticed that my 32 threads (specified in the Add-AzureVHD command) all have latencies of >200 ms. This is far higher than it should be, so I pulled out tcping and tested the latency from the same exact machine to the remote server in question (by IP address) and consistently get <50ms response times. There doesn't seem to be any bottlenecks in this process that I can identify. The SAN is so underworked that it looks like it might fall asleep. The eight cores on the box in question putter around between 0 - 10% usage. I have 14 GB RAM marked as free. There is truly no resource bottleneck.

In all that I suppose I have a couple of questions, but would really appreciate any input that anyone might have on this.

  1. What's with the discrepancy in latency between tcping and Resource Monitor? - UPDATE: Ping times are probably high because I'm saturating the Comcast link with my upload. I don't know why tcping traffic would be prioritized over my Add-AzureVHD command, but I'm starting not to care because there might not be a good reason.
  2. What might be my problem with the super-slow MD5 hash check?
  3. [SOLVED: Comcast didn't provision package correctly.] Aside from the possibility that Comcast failed to actually allocate 20 Mbps upload pipe to me, what could be the cause of the artificially low 10.8 Mbps upload rate?
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  • Are you certain you don't have 100mb nics on your router, firewall, or any other device between your Comcast connection, and the device performing the upload?
    – Zoredache
    Oct 24, 2014 at 16:43
  • I thought about that due to that specific transfer rate, but alas, not the case. I just called Comcast and discovered that they didn't actually successfully provision my package yesterday when I asked them to. They're in the process of doing so now. Now I just have questions about the latency differences and MD5 hash checks.
    – pk.
    Oct 24, 2014 at 16:49
  • MD5 calculation is probably done using Windows Crypto DLL so it is standardized that way. See if the disk or the CPU is the bottleneck (most likely the HDD) and repeat the hashing experiment on a machine with better specs.
    – proteus
    Oct 24, 2014 at 19:58

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