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How do I improve disk IO for XenServer 6.5 and later

Bill Artemik


We manage several XenServer VM hosts for various clients. One thing we have notice with the recent machines is disk I/O performance is poor. The new servers we installed have 500GB SSD RAID and 48 GB RAM. Boot times and file access is as slow as it was with conventional EMD's. We expected SSDs to really improving disk speeds but we're not seeing it.


Are there tweaks we can do to speed up disk I/O? This existing machine we're working on is a XenServer 7.1 machine with 1T of SSD storage. All storage is local. There's only 1 Windows Server 2012 R2 VM running. 4 Cores, 16 GB RAM. It's a new setup so there's really no load but copying files is really slow. Login times are the same as a conventional PC. I don't have any metrics to post but ANY speed improvement would be welcomed. 

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Not really for local storage that I know of. Since you are on 7.1 (I assume LTSR) and latest hotfixes and your XenServer 

Management agent is the latest version I'm not sure what you can do to improve that performance. 


What are you using for disk performance testing? 




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What is your RAID configuration? As with many RAID setups, even SSD drives can only do so much, especially with RAID 5 and 6.

I have a pure SSD RAID5 configuration that does worse with writes than a RAID10 conventional disk setup, in part because the RAID with th espinning disks has many more of them and RAID 10 is much better for I/O - especially writes --  (though twice s expensive!) as RAID 5.



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Not very optimal for writes, though. For optimal write, the I/O still needs to be spread out among multiple disks, even if SSDs. My 4-unit RAID 5 all fast SSD setup is beat by a conventional spinning disk RAID 10 setup because of using a lot of separate drives, which splits up the I.O load more efficiently.


Raid 1 is fine for running the XS operating system, but not so much IMO for getting good I/O for VMs.



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