Hi Paolo et al.
I have a strong suspect that something is going wrong when the
underlying block device responds with a large delay. What makes me
thinking so is that I use a VM on some cloud provider, and they have
substantial block device latency resulting in permanently high (~20%)
iowait. It spikes occasionally when their cluster is overloaded, and
when that happens, the I/O in my VM may stop and never recover. This is
a rare occasion, but it really happens.
What's worse, so far I've seen such a behaviour with BFQ only. I'm still
testing other schedulers though.
Important note: I have no strict evidences that this is *the* case, thus
I'm asking for some suggestions. My idea is to fire up a local VM and
inject delays to a block device while performing some I/O from within
the VM.
So the question is: how can those delays be injected? Using dm-delay?
Can those delays be random?
Thanks in advance.
--
Oleksandr Natalenko (post-factum)
