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

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