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XenServer slow ISCSI Storage Perforamance, no Problems with ESXi

Benjamin Oumlsterle




we are having a PureStorage (AllFlash) Active Cluster with 2 VMware (Huawei 1288H V5) Servers and 2 XenServers (HP DL380 Gen9).

All Servers are connected with 2x 10GbE for the ISCSI Traffic.


The VMware Servers are using 2x 10GbE Ports for all Traffic (Internal, iscsi, dmz, and so on...)

The XenServers are having 2 dedicated ports for the ISCSI Traffic.


With the VMware Servers (Version 6.7) we are reaching:

Read: 105.000 IOPS

Write: 65.000 IOPS


With the XenServers (Version 7.6) we are getting:

Read: 72.000 IOPS

Write: 35.000 IOPS



So why are XenServers slower?


We are not using:

- Link Bonding


- Jumbo Frames


MultiPathing is enabled and working - i can see on the Storage that the XenServers are connected with 4 Paths (2 Paths to ISCSI Network 1, and 2 Paths to ISCSI Network 2)

I used this guide to integrate the Storage:



Can somebody tell me why the XenServers are not having the same Performance like the ESXI Servers?



Kind Regards,


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There could be a lot of reasons. It could be the drivers in XenServer, it could be optimization settings for networking 

that may help with performance, it could be you need more memory allocated to Dom0, and it could just as easily

be that comparing XenServer to VMWare, that it just doesn't have the performance with your given hardware.




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I allocated more ram to dom0 (default4 gb, i allocated 16gb), no change.

i pinned 32 vcpu to dom0, no change. 


The XenServers are on the same core switch with the VMware Servers...



With XenTop i can see that the cpu utilization is jumping the 300-400% when i start an iometer test!


CPU is 2x Intel(R) Xeon(R) CPU E5-2660 v3 @ 2.60GHz


When i do a simple CrystalDiskmark test, im getting over 2000 MBs Read, with the XenServer i get about 1000 MBs.

So i will accept it that the xenserver is a little bit slower, but we are talking about 50%...

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I tried the following things:

In the initial config i had 2 Network Adapters.

Adapter 1:

- Port 1 in LAN / DMZ

- Port 2 in ISCSI Network 1


Adapter 2:

- Port 1 in LAN / DMZ

- Port 2 in ISCSI Network 2


I did now a fresh install of XS 7.6.

Then I changed it that ISCSI Network 1 is on Adapter 2 Port 1, and ISCSI Network 2 is on Adapter Port 2.

No change.


I can identify that when i start a performance test, traffic is running through both interfaces - so mpio is working!

Then i tried to disable one of the interfaces, the speed is nearly the same. Tried the same thing with the other iscsi interface, same speed.


But whats happening with the CPU when i start performance test?

The cpu of dom0 is jumping to over 300%? Could be this the problem?



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