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

Rainer Krienke krienke at uni-koblenz.de
Tue Mar 17 16:58:30 CET 2020


Hello,

thanks for your answer,

if I  understand you correctly, than iothreads can only help if the VM
has more than one disk, hence your proposal to build a raid0 on two rbd
devices. The disadvantage of this solution would of course be that disk
usage would be doubled.

A fileserver VM I manage (not yet productive) could profit from this. I
use LVM on it anyway and I could use striped LVs, so those volumes would
read from more vm pv disks. Should help I guess.

The hosts CPU is a AMD EPYC 7402 24-Core Processor. Does it make sense
to select a specific CPU-type for the VM. My test machines have a
default kvm64 processor. The number of processors should then probably
be minimal equal to the number of disks (number of iothreads)?

Do you know if it makes any difference wheater I use the VirtIO
SCSI-driver versus the Virtio-SCSI-single driver?

Thank you very much
Rainer

Am 17.03.20 um 14:10 schrieb 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
> 
> 

-- 
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
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