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

[Eneko Lacunza]

Hi,

You can try to enable IO threads and assign multiple Ceph disks to the 
VM, then build some kind of raid0 to increase performance.

Generally speaking, a SSD based Ceph cluster is considered to perform 
well when a VM gets about 2000 IOPS, and factors like CPU 1-thread 
performance, network and disk have to be selected with care. Also 
server's energy saving disabled, etc.

What CPUs in those 9 nodes?

Ceph is built for parallel access and scaling. You're only using 1 
thread of your VM for disk IO currently.

Cheers
Eneko

El 17/3/20 a las 14:04, Rainer Krienke escribió:
> 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


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