Re: [linux-iscsi-devel] [PATCH} remove portal failover from iscsi driver

[Mike C. <mi...@us...>]

Dan Bar Dov wrote:
> So, your answer summerized is - we remove portal failover now, because
> someday in the future there will be an alternative.
> 

That is not twisting things too much. It really depends on how much
time you spent looking into things like dm, and how you interpret when
Cisco marks some driver versions as experimental. You also forgot the
part where some FUD was cleared up ;)

What makes you think we will be done before dm? How far off
do you tihnk dm-multipath is? I know you just got a chance to
look at it since you were posting about something else
previously, but are we talking weeks, months?

> I think this is a very bad decision: iSCSI is catching on. Linux-iscsi
> is the de-facto standard initiator in the Linux world. Serious storage
> users "must" have failover functionality - and the current portal
> failover does provide such functionality, even better, it works.
> 
> So by removing this feature now without supplying a tested/working
> alternative, we are setting iSCSI back. 
> 

Is your concern that we will get a iscsi driver in mainline
and dm multipath will not be there and the driver will have
had its failover removed too? Or are you concerned that
that between the time we are both trying to get into
the kernel that we will have sourceforge drivers with
no failover? Are you concerned about the distro versions
of the driver?


> I seriously recommend against taking this functionality out right now. 


> Dan
> 
> 
>>-----Original Message-----
>>From: Mike Christie [mailto:mi...@us...] 
>>Sent: Thursday, November 25, 2004 11:53 PM
>>To: Dan Bar Dov
>>Cc: krm...@ci...; lin...@li...
>>Subject: Re: [linux-iscsi-devel] [PATCH} remove portal 
>>failover from iscsi driver
>>
>>Dan Bar Dov wrote:
>>
>>
>>>Which multipath drivers were tested to work with iscsi and 
>>
>>provide the 
>>
>>>same/similar functionality as portal failover?
>>>
>>
>>None. dm-multipath is the future of multipath for Linux 
>>though (well maybe not completely for iscsi, but that is a 
>>long way off). dm-multipath was tested, but not thoroughly.
>>
>>
>>>If you export all paths, it means there's a 
>>
>>multi-connection session, 
>>
>>>and by using an active-passive mp you some of the connections are 
>>>simply
>>
>>Is this comment about block layer multipath or the driver. I 
>>do not think the driver does multi-connection sessions, and 
>>if you use dm then there will be a connection per session 
>>(look through linux-scsi for why that is so).
>>
>>Also, for dm who said you must do active-passive? Are you 
>>thinking about md?
>>
>>
>>>dormant running NOPs. Also, you need to communicate 
>>
>>death/revival of 
>>
>>>paths to the multipath driver?
>>>
>>
>>Today, dm-multipath's userspace component path tester will 
>>send IO to the paths to try and detect this.
>>
>>If you want to make it more iscsi specific and just send a 
>>nop, implement a callout for the userspce tools. I was going 
>>to add a sysfs attr so the userspace tools could do this. Or 
>>maybe a litte farther off, within the driver when we detect 
>>this we can kick to userspace and dm-mutipath's tools can be 
>>made to handle this (this is a long way off though since we 
>>do not have userspave event capabilites just yet).
>>
>>here are some old dm docs. http://christophe.varoqui.free.fr/
>>
>>
>>>Dan
>>>
>>>
>>>
>>>>-----Original Message-----
>>>>From: lin...@li...
>>>>[mailto:lin...@li...] On Behalf Of 
>>>>N.C.Krishna Murthy (krmurthy)
>>>>Sent: Tuesday, November 23, 2004 9:15 PM
>>>>To: lin...@li...
>>>>Subject: [linux-iscsi-devel] [PATCH} remove portal failover 
>>
>>from iscsi 
>>
>>>>driver
>>>>
>>>>Hi,
>>>>	It was decided that portal failover has to be removed 
>>
>>from iSCSI 
>>
>>>>driver.
>>>>All the available paths have to be exported so that 
>>
>>multipath drivers 
>>
>>>>can use them.
>>>>
>>>>The attached patch removes portal failover from kernel files. 
>>>>After applying the patch the driver establishes one session per 
>>>>path(TargetAddress).
>>>>
>>>>Very minimal user level cleanup has been done. Will futher provide 
>>>>patches that
>>>>A) cleanup Portal failover stuff in user mode
>>>>B) document the new behaviour.
>>>>
>>>>Could you please review this patch and let me know?
>>>>
>>>>Thanx
>>>>NCKM
>>>>
>>>>
>>>>
>>>
>>>
>>>
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>>
>>
> 
> 
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