[PVE-User] Proxmox with ceph storage VM performance strangeness

[Rainer Krienke]

Hello,

I run a pve 6.1-7 cluster with 5 nodes that is attached (via 10Gb
Network) to a ceph nautilus cluster with 9 ceph nodes and 144 magnetic
disks. The pool with rbd images for disk storage is erasure coded with a
4+2 profile.

I ran some performance tests since I noticed that there seems to be a
strange limit to the disk read/write rate on a single VM even if the
physical machine hosting the VM as well as cluster is in total capable
of doing much more.

So what I did was to run a bonnie++ as well as a dd read/write test
first in parallel on 10 VMs, then on 5 VMs and at last on a single one.

A value of "75" for "bo++rd" in the first line below means that each of
the 10 bonnie++-processes running on 10 different proxmox VMs in
parallel reported in average over all the results a value of
75MBytes/sec for "block read". The ceph-values are the peaks measured by
ceph itself during the test run (all rd/wr values in MBytes/sec):

VM-count:  bo++rd: bo++wr: ceph(rd/wr):  dd-rd:  dd-wr:  ceph(rd/wr):
10           75      42      540/485       55     58      698/711
 5           90      62      310/338       47     80      248/421
 1          108     114      111/120      130    145      337/165


What I find a little strange is that running many VMs doing IO in
parallel I reach a write rate of about 485-711 MBytes/sec. However when
running a single VM the maximum is at 120-165 MBytes/sec. Since the
whole networking is based on a 10GB infrastructure and an iperf test
between a VM and a ceph node reported nearby 10Gb I would expect a
higher rate for the single VM. Even if I run a test with 5 VMs on *one*
physical host (values not shown above), the results are not far behind
the values for 5 VMs on 5 hosts shown above. So the single host seems
not to be the limiting factor, but the VM itself is limiting IO.

What rates do you find on your proxmox/ceph cluster for single VMs?
Does any one have any explanation for this rather big difference or
perhaps an idea what to try in order to get higher IO-rates from a
single VM?

Thank you very much in advance
Rainer



---------------------------------------------
Here are the more detailed test results for anyone interested:

Using bonnie++:
10 VMs (two on each of the 5 hosts) VMs: 4GB RAM, BTRFS, cd /root;
bonnie++ -u root
  Average for each VM:
  block write: ~42MByte/sec, block read: ~75MByte/sec
  ceph: total peak: 485MByte/sec write, 540MByte/sec read

5 VMs (one on each of the 5 hosts) 4GB RAM, BTRFS, cd /root; bonnie++ -u
root
  Average for each VM:
  block write: ~62MByte/sec, block read: ~90MByte/sec
  ceph: total peak: 338MByte/sec write, 310MByte/sec read

1 VM  4GB RAM, BTRFS, cd /root; bonnie++ -u root
  Average for VM:
  block write: ~114 MByte/sec, block read: ~108MByte/sec
  ceph: total peak: 120 MByte/sec write, 111MByte/sec read


Using dd:
10 VMs (two on each of the 5 hosts) VMs: 4GB RAM, write on a ceph based
vm-disk "sdb" (rbd)
  write: dd if=/dev/zero of=/dev/sdb bs=nnn count=kkk conv=fsync
status=progress
  read:  dd of=/dev/null if=/dev/sdb bs=nnn count=kkk  status=progress
  Average for each VM:
  bs=1024k count=12000: dd write: ~58MByte/sec, dd read: ~48MByte/sec
  bs=4096k count=3000:  dd write: ~59MByte/sec, dd read: ~55MByte/sec
  ceph: total peak: 711MByte/sec write, 698 MByte/sec read

5 VMs (two on each of the 5 hosts) VMs: 4GB RAM, write on a ceph based
vm-disk "sdb" (rbd)
  write: dd if=/dev/zero of=/dev/sdb bs=4096k count=3000 conv=fsync
status=progress
  read:  dd of=/dev/null if=/dev/sdb bs=4096k count=3000  status=progress
  Average for each VM:
  bs=4096 count=3000:  dd write: ~80 MByte/sec, dd read: ~47MByte/sec
  ceph: total peak: 421MByte/sec write, 248 MByte/sec read

1 VM: 4GB RAM, write on a ceph based vm-disk "sdb" (rbd-device)
  write: dd if=/dev/zero of=/dev/sdb bs=4096k count=3000 conv=fsync
status=progress
  read:  dd of=/dev/null if=/dev/sdb bs=4096k count=3000  status=progress
  Average for each VM:
  bs=4096k count=3000:  dd write: ~145 MByte/sec, dd read: ~130 MByte/sec
  ceph: total peak: 165 MByte/sec write, 337 MByte/sec read
-- 
Rainer Krienke, Uni Koblenz, Rechenzentrum, A22, Universitaetsstrasse  1
56070 Koblenz, Web: http://www.uni-koblenz.de/~krienke, Tel: +49261287 1312
PGP: http://www.uni-koblenz.de/~krienke/mypgp.html,     Fax: +49261287
1001312