Slow files server write speeds over the network

[Helios Comms]

Setup: a pretty simple three server system: domain controller, file server and XenApp server on a single virtual network with a virtual gateway to allow remote access via XenApp.

Problem: users on XenApp are reporting very slow file access, esp. in Sage. It's got noticeable worse.

Diagnostics carried out: copy 512MB test file between the various servers:

1. XenApp server to file server: horrible 600KB/s (so writes across virtual network are slow)
2. File Server to XenApp server: acceptable 50MB/s (so reads are fine)
3. File Server to File Server local copy: 20MB/s which is expected due to read/write
4. Download of 1GB file from web browser on file server: very slow, like 1.5 hours
5. XenApp server to domain controller: acceptable 40MB/s

So I surmise here that everything is fine except data coming in through the network. Write speeds on the file server are okay. Reads from file server to other are fine.

Any ideas how I go about isolating the fault?

[#2]

PS. Client unfortunately doesn't have support contract with Microsoft otherwise I'd raise a ticket. I'm just checking whether you can buy support for just a month...

[#3]

I think what would be helpful is to understand if these machines were migrated or if they were existing image VHD's that were turned on in Azure. Also could you list out the size of VM's and disk sizes that you have provisioned? One thing you can also run is the performance diagnostics on the individual VMs. This is done from the VM blade under support and troubleshooting. It would also be very helpful if you could share those results. 

@Helios Comms