Slow transfers between DSM VM and Windows VM

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So. First of all, here is my setup :

  • HP Proliant Gen 8 Server
  • Xeon e3-1220 V2 
  • 16 GB RAM
  • IBM M1015 (flashed in IT mode) controler card. 
  • 4 big disks plugged on SAS port 0 on the controller card.
  • 1 SSD plugged on one free SATA connector on the motherboard (I believe it is for optical drive)


I installed ESXI 6.7 - the HP version ("HPE Custom Image for ESXi 6.7 GA").


I was able to migrate my baremetal install of DSM to a VM one (with Jun's Loader v1.03b DS3615xs). I did not passtrought the HBA card. Just each disk as "raw disk" (RDM).


Accessing to my DSM share though the network is somewhat similar to what it was bare-metal. Speed is ok from my Macs using either SMB or AFP protocols. So, I think I have no problem here.


I've also created a Windows 10 VM. I've had to use Windows Enteprise because I need remote desktop and it's no longer in the "Family" branch (took  me a while to figure this one out). So I have latest Win10 Ent LTSB N. It works ok (I think). However, when I mount one of my DSM share. Transfers are slow and unstable. Which defeats the purpose of having a Windows VM running alongside the NAS VM in the same host.


I may have missed something in the network settings.

I have both my NICs connected to one Vswitch. I have one "port group" (can't remember the name) for DSM. Another one for Windows VM. 

Both VMs have a network adapter in VMXNET3.

Edited by kouignamann
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How are your disks configured? Any sort of Raid?

If I'm reading things correctly, you're copying files to shares between 2 VMs that might be on the same set of disks.. That's gonna vastly reduce your speeds.. Try hosting one VM on one disk and another on a separate disk, out of interest.. Thick provision your storage too..

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The two VMs uses different disks/controllers.

Apart from the tiny virtual boot drive, DSM VM uses 4 disks on the HBA card. 3 of them are managed as a RAID volume by DSM.

Windows VM uses a virtual disk in ESXI datastore. The datastore is stored on a SSD, connected to a SATA port on the motherboard. I don't know how fast is this SATA port.

Edited by kouignamann
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23 minutes ago, Hostilian said:

Are the datastores thin provisioned


Which means? It the virtual disk large enough? Or, is it a specific setting I may have missed?


I tested again last night :

  1. I logged into my Windows VM with Remote Desktop
  2. I connected one of my DSM share as a network drive.
  3. Browsing through the folders of the share is normal and I see no lag.
  4. I use the Windows 10 ISO file as a test file (about 4GB). 
  5. Transfers started arround 30MBps and immediatly drops to a few hundreds KBps and zero.
  6. Once it gets to zero (it took less than ten seconds) I canceled the file copy and I was barely able to browse the share. 
  7. I couldn't even copy a small image file to the share.

I also ran Adobe Lightroom on the Windows VM to test an image export. It was unable to export anything as the export job froze at 0%. Indicating it cannot access the source files on the share.

Which is even worse than when I first tested it (same ISO file). On earlier tests, the copy speed waas very unstable between 10 and 40 MBps but did not drop to zero.


Worth mentioning. I the meantime my laptop was connected to a DSM share and everything was very fast and snappy. I just noticed a glitch. I was playing a video file in VLC from a DSM share and it froze when the Windows VM started. 



For the sake of testing things. I opened "speedtest" website in Windown VM internet browser to test internet speed. I got 800 Mbps down (I have fast internet at home) but upload test failed (weird again).


I don't know where the bottleneck is. 

Edited by kouignamann
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Windows VM is "Thick provisioned, lazily zeroed"


DSM was migrated to a new install. VM Tools installed (with Synology Package Center).

Windows VM has VM Tools as well. 

ESXI is latest HP custom image.


Below a screenshot of a file transfer. And my vSwitch config.


Capture d’écran 2018-10-05 à 19.24.21.png

Edited by kouignamann
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So I've done some more testing.


I don''t think this is a write caching issue since I'm reading files from a volume on the HBA card and writing on a regular SSD on a separate SATA port.


First thing first. My transfers speed between a regular computer on the network (my Mac) and the DSM vm are normal. I get about the same speeds as in bare-metal. 


Not the same story when I use the Windows VM instead of a computer.

  • My datastore is connected to the optical drive SATA port on the motherboard. Maybe it was slow. So I've connected it to the SAS port of the motherboard (can"t boot from HBA card). 
    No improvement.
  • I tried using a dedicated SSD connected to the second SAS port of my HBA card and using this disk (as RDM disk) with windows VM. To see if it is a thick provisionning thing.
    No improvement.
  • I tried a regular Windows 10 family instead of Windows 10 Ent. LTSB. To see if I have a windows issue.
    No improvement.
  • I tried disabling all firewalls and all in the windows VM. 
    No improvement.

I need to do some more testing. I'm no longer sure my read/write speeds are good with a regular computer (MacOS doesn't display transfer speeds).


Again, could it be a wetwork thing. I feel like It doesn't balance the load very well between users connected to the DSM VM. Once the Windows VM is started, even if it has close to zero network activity. My transfer speeds with DSM shares are lower.

Edited by kouignamann
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Tested again. 


Enabled jumbo frames on the vSwitch, DSM network config and Windows network config. No noticeable improvement.


I passed through my HBA card as a PCI device instead of passing each disk with RDM.  Now I get between 50 MB/s and 500 MB/s transfer speeds. I like it better.


I have spare SSD lying arround, I'll try enabling SSD cache in DSM to see if I get better results.

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