[dm-devel] Problems with multipathing

[Christophe Varoqui]

Roger Håkansson a écrit :
> Roger Håkansson wrote:
>   
>> With upstream I guess you mean 0.4.7 or "CVS-HEAD".
>>
>> Haven't tried that, but just looking at the requirements tells me I'll
>> have a lot to do in order to even just to prepare to test it.
>>
>>     
>>>  Dependencies :
>>>  Linux kernel
>>>
>>>      * 2.6.10-rc*-udm2 or later
>>>      * 2.6.11-mm* or later
>>>      * 2.6.12-rc1 or later
>>>  udev 050+
>>>       
>> CentOS 4.3 have 2.6.9-34 and udev-039-10, and even though some stuff are
>> backported I guess I have to update both and I can only imagine the
>> amount of work that will render me, but I'll try to do it if I can find
>> the time...
>>
>> 	
>>     
>
> 0.4.7 seems to work better without updating kernel or udev, but not
> entirely...
>
> Unless I've gotten this wrong, with pathgroupingpolicy set to failover I
> should get two pathgroups where only one is active an if the active
> fails, the other pathgroup will become active, correct?
> Multibus pathgrouping will place all paths in the same pathgroup so that
> all paths will share the I/O when they are active and if some path
> fails, the I/O is spread among the active paths, correct?
>
> Multibus works just like I expect it to, but failover doesn't fail the
> path entirely.
>
> This is what 'multipath -ll' gives me after I have disconnected one HBA
> from the fabric.
>
> mpath1 (3600d0230000000000b0191489a946602)
> [size=183 GB][features=0][hwhandler=0]
> \_ round-robin 0 [prio=0][enabled]
>  \_ 1:0:1:1 sdc 8:32  [active][faulty]
> \_ round-robin 0 [prio=0][enabled]
>  \_ 2:0:0:1 sdf 8:80  [active][ready]
> mpath2 (3600d0230000000000b0191489a946600)
> [size=97 GB][features=0][hwhandler=0]
> \_ round-robin 0 [prio=0][active]
>  \_ 1:0:1:0 sdb 8:16  [failed][faulty]
>  \_ 2:0:0:0 sde 8:64  [active][ready]
>
> Notice that sdc is faulty, but still active and both pathgroups are
> enabled but none is active...
>
> I've noticed this problem when I/O is active ( I was running a 'dd
> if=/dev/zero of=/mount_point count=10000000000' to each mpath) when one
> "path" fails, if there is no activity at all the failover works.
>
>   
I don't know your hardware (vendor = IFT, product = A16F-R2221) but it 
seems assymmetrical. Most hardware in this familly need a hardware 
handler, and some need the "queue_if_no_path" feature set too.

You'll have to find how your array works and try to figure if some 
existing hardware handler does the good thing.

As a last resort, post the maximum techical details about what  your 
hardware needs to activate backup paths, and hope that some good soul is 
willing to code the handler.

Regards,
cvaroqui