Hi everyone!
Two years ago I worked on many features in the Xen Orchestra project like delta backup algorithm, load balancing, ...
After all this time, I'm back to contribute to XCP-ng. 
Currently, I'm working on performance improvements (VM migration, storage...) and on new SMAPIv3 plugins.
And maybe in the future on other cool stuff. 
Ronan
Here are some new charts. Make sure you understand the global QCOW2 image structure. (See: https://events.static.linuxfound.org/sites/events/files/slides/kvm-forum-2017-slides.pdf)
More explicit labels :
These results where obtained with an optane (nvme). We can see a better random write performance with the F configuration instead of using the default qemu-dp parameters and the ioping is not so bad. But it's not sufficient compared to tapdisk.
So like said in the previous message, it's the moment to find the bottleneck in the qemu-dp process.
Thank you to flamegraph. (See: http://www.brendangregg.com/FlameGraphs/cpuflamegraphs.html)
Analysis and improvements in a future message!
After some investigation, it was discovered that the SMAPIv3 is not THE perfect storage interface. Here are some charts to analyze:
Yeah, there are many storage types:
You can notice the usage of RAID0 with ext4-ng, but it's not important for the moment.
Let's focus on the performance of ext4-ng/xfs-ng! How can we explain these poor results?! By default the SMAPIv3 plugins like gfs2/filebased added by Citrix use qemu-dp. It is a fork of qemu, it's also a substitute of the tapdisk/VHD environment used to improve performance and remove some limitations like the maximum size supported by the VHD format (2TB). QEMU supports QCow images to break this limitation.
So, the performance problem of the SMAPIv3 seems related to qemu-dp. And yes... You can see the results of the ext4-ng VHD and ext4-ng VHDv1 plugins, they are very close to the SMAPIv1 measurements:
Next, to validate a potential bottleneck in the qemu-dp process, two RAID0 have been set up (one with 2 disks and an other with 4), and it seems interesting to see a good usage of the physical disk! There is one qemu process for each disk in our VM, and the disk usage is similar of the performance observed in the Dom0.
The SMAPIv3/qemu-dp tuple is not totally a problem:
Next steps:
@peder Fixed! This fix will be available (as soon as possible) in a future xcp-emu-manager package.
@swivvle You can create a ext4 SR like this:
xe sr-create type=ext4-ng name-label=sr-test device-config:device=/dev/sda3
For a basic filebased SR:
xe sr-create type=filebased name-label=sr-test2 device-config:file-uri=/root/sr-folder
Don't hesitate if you have other questions.
It seems to be supported by the XAPI:
https://github.com/xapi-project/xen-api/blob/master/ocaml/xapi/cli_operations.ml#L833-L837
https://xapi-project.github.io/xen-api/classes/pool.html#enable_ha
SR ref set heartbeat_srs: Set of SRs to use for storage heartbeating
Did you tried this command?
@swivvle What's your exact command line? Have you restarted the toolstack?
@swivvle You can create a ext4 SR like this:
xe sr-create type=ext4-ng name-label=sr-test device-config:device=/dev/sda3
For a basic filebased SR:
xe sr-create type=filebased name-label=sr-test2 device-config:file-uri=/root/sr-folder
Don't hesitate if you have other questions.
@peder Fixed! This fix will be available (as soon as possible) in a future xcp-emu-manager package.
@Kalloritis I'm not sure about that. You see a stack of "unknown" functions because the tapdisk binary was not compiled with all debug symbols, contrary to qemu-dp.
And I'm waiting for the next XenServer release before continuing this diary.
Thank you to flamegraph. (See: http://www.brendangregg.com/FlameGraphs/cpuflamegraphs.html)
Analysis and improvements in a future message!
Here are some new charts. Make sure you understand the global QCOW2 image structure. (See: https://events.static.linuxfound.org/sites/events/files/slides/kvm-forum-2017-slides.pdf)
More explicit labels :
These results where obtained with an optane (nvme). We can see a better random write performance with the F configuration instead of using the default qemu-dp parameters and the ioping is not so bad. But it's not sufficient compared to tapdisk.
So like said in the previous message, it's the moment to find the bottleneck in the qemu-dp process.
After some investigation, it was discovered that the SMAPIv3 is not THE perfect storage interface. Here are some charts to analyze:
Yeah, there are many storage types:
You can notice the usage of RAID0 with ext4-ng, but it's not important for the moment.
Let's focus on the performance of ext4-ng/xfs-ng! How can we explain these poor results?! By default the SMAPIv3 plugins like gfs2/filebased added by Citrix use qemu-dp. It is a fork of qemu, it's also a substitute of the tapdisk/VHD environment used to improve performance and remove some limitations like the maximum size supported by the VHD format (2TB). QEMU supports QCow images to break this limitation.
So, the performance problem of the SMAPIv3 seems related to qemu-dp. And yes... You can see the results of the ext4-ng VHD and ext4-ng VHDv1 plugins, they are very close to the SMAPIv1 measurements:
Next, to validate a potential bottleneck in the qemu-dp process, two RAID0 have been set up (one with 2 disks and an other with 4), and it seems interesting to see a good usage of the physical disk! There is one qemu process for each disk in our VM, and the disk usage is similar of the performance observed in the Dom0.
The SMAPIv3/qemu-dp tuple is not totally a problem:
Next steps:
Hi everyone!
Two years ago I worked on many features in the Xen Orchestra project like delta backup algorithm, load balancing, ...
After all this time, I'm back to contribute to XCP-ng.
Currently, I'm working on performance improvements (VM migration, storage...) and on new SMAPIv3 plugins.
And maybe in the future on other cool stuff.
Ronan