RE: Read Performance issue when Xen Hypervisor is activated

[Michael Schinzel <schinzel@ip-projects.de>]

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We have searched in the last days more and more for the cause of this performance issue.

In cooperation with the datacenter, we change some hardware to check, if the problem already proceeds. We put the RAID Controller included all RAID Arrays to another Supermicro Mainboard: X10SLM-F with only one CPU. The result was, we got 400 MB/s read Speed. So it seems there is an issue with the Servers Mainboard / CPU and the Xen Hypervisor but, we also change the Mainboard to an Supermicro X9DR3-F with the actual BIOS Version 3.2a - these also do not solved the problem with the performance.

What we also have done:

-          Upgraded Hypervisor from default Debian 8 - 4.4.1 to 4.8.

-          Tested some kernel boot configurations

With an non hypervisor Kernel, the system also uses the read Cache of the controller and after some read operations at the same file, it gets 1.2 G/s back from the Cache. At Xen Hypervisor Kernel, it seems the system do not use any caching operations. I also tested a bit with hdparm:

root@v7:~# hdparm -Tt /dev/sdb

/dev/sdb:
Timing cached reads:   14060 MB in  1.99 seconds = 7076.16 MB/sec
Timing buffered disk reads: 304 MB in  3.01 seconds = 100.85 MB/sec

This Performance is horrable. It is a RAID 10 with read/write cache and SSD Caching functions.

Does somebody know how Xen proceeds with such Caching Systems?


Yours sincerely

Michael Schinzel



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