limiting writes / reads with Read limit (MB/s) - proxmox GUI

[felipe]

HI,

i would like to limt some maschines with the cool io limit feature of proxmox. (kvm)
I tried put 70 and 70 for Write limit (MB/s) and Read limit...
And 70 also for Read limit iops
But then the server is getting verrrrry slow.

is the problem the iops? but 70 should not be bad? or am i totally wrong? a sata disk should have normally between 100 - 120 iops- so it still should have 50% of a sata disk performance...

please help.

best regards
philipp

 

[snowman66]

hi,

i guess iops are a little more complicated - the rate 100-120 iops doesn't tell you much in this case.
Run some test with iometer and you'll see that rate can go above 20k iops.

For more infos: http://www.brentozar.com/archive/2013/09/iops-are-a-scam/

 

[felipe]

hmmm i know that iops is generally complicated related with 4k, 64k, troughuotput and so on...
but what options can i set then to limit bandwith of hd? i want for example halv of the speed of a normal sata disk...
looks like a nice feature. and in future we will use ceph- but i dont want users, viruses, hacks or whatever to take to much io from the ceph cluster...

does anybody use this feature?

 

[felipe]

i was testing and the config of mb/s gives me more or less the speed exspected in cristal diskmark...

but the iops config not:
for the 512k test:
MBps

= (IOPS * kb) / 1024
70 * 512 / 1024 should give me 35MB/s but i get less then the half. and writethrough the same. very poor speed.​

 

[snowman66]

See also:
http://wiki.qemu.org/Features/DiskIOLimits
http://pve.proxmox.com/pipermail/pve-devel/2013-December/009290.html
http://pve.proxmox.com/pipermail/pve-devel/2013-December/009293.html