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Slow disk operations on guest VM on XenServer 7.3

Ilya Egorov




I've installed XnServer 7.3.0 on a brand new one Dell PowerEdge R320 which has 1 CPU x Intel Xeon E3-1220 v6 @ 3.00Ghz server. As a guest VM I've installed Windows Server 2016 Standart 64-bit with XenServer Tools installed on it. Everything seems to be fine, except that the guest VM is extremely SLOW, despite I've allocated 16Gb or RAM (32Gb total), and it has got 4 vCPUs, 1 socket with 4 cores per socket, and it has the highest priority for this VM. I found out that the VM is actually has a lot of CPU resources, it's almost idle all the time, as well as it has got a lot of free memory, but the disk operations is what makes it running extremely slow - the hard disk has 100% disk usage almost all the time, so I guess that is the case of my issues. Any file operation takes a lot of time and is visually noticeable. Even opening a window takes more time than usual, despite that the CPU has only a few percents or usage.


On the general tab of the VM in the XenCenter mentioned, that "this VM is not using read caching, because this pool is not licensed for read caching". Is that the reason to my issues? What's the point of the free version then?


Any help would be MUCH appreciated! 

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Update: It turned up that this issue shows up only in console mode in XenCenter application for Windows. Everything's fine when connecting to the VM through RDP. Well, I can deal with that as I don't need  to access the console much often, but I don't think it should be that way though.

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On 30/01/2018 at 6:46 PM, Tobias Kreidl said:

Need more information about your storage: Is it internal, external, what RAID configuration does it have, is it iSCSI/FC/LVM/, what kind and how many drives are in the volume,  how many VMs share that same volume/SR, etc. etc.



The storage is internal, uses LVM, there's only one drive in the volume and only one VM there. The physical drive is 1TB 7200RPM and has 32MB cache.

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Hi everybody

I've a similar issue.

Hp Proliant DL360 GEN10 4110  1 Xeon 8-Core 4110 - 16Gb Ram - Controller HPE Smart Array P408i-a SR Gen10 for 4 SAS HDD 15K 300Gb (raid 1+0)

Xen Sever 7.6 + Xen Tools


I noticed slow performance with the VM (windows 2016 Standard)


I ran some tests with Passmark PerformanceTest 9

I had these results :

Disk Seq Read 951

Disk Seq Write 895

Disk random seek + write 933


same test, on a phisical windows machine, on a identical server, gives : 

Seq Read 3593

Seq Write 3646

Random seek + write 3365


Can you help me to understand why ? thank you very much


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