Environment:
vSphere 5.5
Datastore local
Network: 3 vmnics with link aggregation
I noticed that copying large files (4,4GB) in Windows 7 VM starts really fast with 100 MB/s, but then slows down to 5 MB/s after a while. So the average speed is up to 30 MB/s.
I copy the file from an external samba server (ubuntu 16.10) to this Windows 7 VM, and as another test from another Windows 7 real PC. Same results.
But if I copy this large file from the external samba server to a virtual samba server on the same host as the Windows 7 VM the average throughput is ~97/107 MB/s.
The virtual samba server is connect to the same 3 vmnics as the Windows 7 VM, but uses a E1000 nic.
On the Windows 7 VM i tried several things for tuning:
change the nic from vmxnet3 to e1000
configure TCP_Offload
disable autotuning
large files enabled in registry
changed SCSI Controller (VM)
and serveral other things with no acceptable result.
In vSphere client I can monitor the performance of the virtual disks:
Windows 7 up (starting with ~ 60 000 kb/s) and down (5 000 kb/s) and up (30 000 kb/s) and down and up ....
Ubuntu up (at ~ 100 000 kb) and ready after a while.
Copying FROM this VM is no problem, full performance anyway.
Is Windows 7 caching this file before writing to disk?
I noticed that after starting copying task manager shows RAM cache growing till maximum. After reaching maximum copying slows down ...
If caching in RAM maybe VMware host is caching this to disk?
