On 09/10/2009 05:23 PM, Chiradeep Vittal wrote:
> Thanks. I'll take a look at the netlink interface. Not using multipath
> for now, but will do so later.
>
> For basic monitoring of storage network problems, here's what I am
> thinking:
> 1. If there is a network failure, eventually cat /sys/block/<disk>/
> device/state should show "offline" ?
> 2. How long will this take? I know that this is a function of
> replacement_timeout, noop_interval, noop_timeout and scsi timeout, but
> the relationship is not clear
>
> Let us say
> a=session.timeo.noop_out_interval=5
> b=session.timeo.noop_out_timeout=5
> c=session.timeo.replacement_timeout=120
> d=`cat /sys/block/<disk>/device/timeout`=60
>
> The disk should go offline in a maximum of a+b+c+d=190s after a
> network failure?

It is not really that easy, because if the nop times out the iscsi layer 
will drop the session and the disk state will not change to offline. The 
disk state will only change if the scsi command timer fires and the scsi 
eh runs and fails. In this case the disk state will go to offline.

For the nop timeout case and the scsi eh failing case, the iscsi session 
state will go to failed, so you could check that instead. That value is in

/sys/class/iscsi_session/session%SID/state


>
> If the network comes back up, how soon will the disk state go to
> 'running' ?

When the iscsi session is dropped due to a nop timeout or the scsi eh 
failing, the initiator will basically poll the network ever couple of 
seconds by trying to reconnect the tcp connection. And so it depends on 
the type of failure. If the initiator is trying to reconnect the tcp 
connection when the network comes up, then we could reconnect right 
away, or if the network layer cannot figure things out the reconnect 
could timeout and then the next try would work, or if the network had 
given us a error right away when we tried the reconnect then it on the 
next reconnect attempt we would be successful.



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