On 16 Feb 2009 at 12:36, Mike Christie wrote:

> Ulrich Windl wrote:
> > Hi,
> > 
> > my apologies if this was asked and answered before, but I just tried to get 
> > a 
> > HOWTO on iSCSI and multipath, but failed to find something really usable.
> > 
> > I have a question regarding various timeouts, specifically (SCSI command, 
> > TCP 
> > connection, multipath). Somehow those timeout s are hierarchical, meaning 
> > the 
> > multipath daemon (or kernel module) will send some command to a virtual 
> > SCSI 
> > device (iSCSI here), then the iSCSI layer will send a TCP packet on the 
> > wire, and 
> > after some further unpacking a more or less real SCSI device will receive a 
> > command.
> > 
> > If I name those timeouts tm (multipath), tt (TCP), and ts (SCSI) 
> > respectively, 
> > should the following be true:
> > 
> > tm < tt < ts
> > 
> > Or should the exact opposite be true:
> > 
> > tm > tt > ts
> Are you using dm-multipath? If so what timeout are you referencing?
> I tried to document what I think you are asking in the section 8 of the 
> README. Does that help?

Hi Mike and others!

I'm about examining multipath, and the timeouts were still all default. I was 
worrying about the timeout for the path checkers: if it takes a minute (just 
example) to detect that a path is not usable, I/O might also hang for a minute.

Then if the packet to query the multipath status was committed to TCP for 
transport, and the network had a problem, TCP might be able to recover. So if 
timeout for the patch checker is too small (5 seconds, for example), link 
may be changed unneccessarily. I'm trying to get my thoughts clear on that.

In my version of README (/usr/share/doc/packages/open-iscsi/README of SLES10 
the section 8 is labelled "8. iSCSI System Info", and it doesn't mention 


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