On Fri, Aug 3, 2018 at 12:12 PM <Aleksey.I.Maksimov@yandex.ru> wrote:
Hello

I deployed a dedicated server (fs05.holding.com) on CentOS 7.5 and created a VDO volume on it.
The local write test in the VDO volume on this server gives us an acceptable result

# dd if=/dev/zero of=/mnt/vdo-vd1/nfs/testfile count=1000000
1000000+0 records in
1000000+0 records out
512000000 bytes (512 MB) copied, 6.26545 s, 81.7 MB/s

This is not a good test for copying images:
- You are not using direct I/O, and
- You are using block size of 512 bytes, way too small
- You don't sync at the end of the transfer
- You don't copy real image, reading zeros does not take any time, while
  reading real image takes time. This can drop dd performance in half

A better way to test this is:

    dd if=/path/to/src of=/path/to/dst bs=8M count=1280 iflag=direct oflag=direct conv=fsync status=progress 

This does not optimize copying sparse parts of the image. For this you can use
qemu-img, what oVirt is using.

The command oVirt uses is:

    qemu-img convert -p -f raw|qcow2 -O raw|qcow2 -t none -T none /paht/to/src /path/to/dst

The disk capacity of the VDO volume is connected to the oVirt 4.2.5 cluster as the Export Domain via NFS.

I'm seeing a problem with the low performance of Export Domain.
Snapshots of virtual machines are copied very slowly to the Export Domain, approximately 6-8 MB/s.

This is very very low throughput.

Can you give more details on
- the source domain, how it is connected (iSCSI/FC)?
- the destination domain, how is it connected? (NFS 4.2?, 1G nic? 10G nic?)
- the source image - can you attach output of:
  qemu-img map --output json /path/to/src
- If the source image is on block storage, please copy it to a file system
  supporting sparsness using NFS 4.2 using:
  qemu-img convert -p -f raw -O raw -t none -T none /path/to/src/ /path/to/dst
  (if the image is qcow2, replace "raw" with "qcow2")
 

At the same time, if I try to run a write test in an mounted NFS-directory on any of the oVit cluster hosts, I get about 50-70 MB/s.

# dd if=/dev/zero of=/rhev/data-center/mnt/fs05.holding.com:_mnt_vdo-vd1_nfs_ovirt-vm-backup/testfile count=10000000
10000000+0 records in
10000000+0 records out
5120000000 bytes (5.1 GB) copied, 69.5506 s, 73.6 MB/s

Again, not a good way to test.

This sounds like https://bugzilla.redhat.com/1511891.
(the bug may be private)

Finally, can you provide detailed commands to reproduce your
setup, so we can reproduce it in the lab?
- how to create the vdo volume
- how you created the file system on this volume
- NFS version/configuration on the server
- info about the server
- info abut the network
- info about the host

Nir