[dm-devel] Setting up a multipath device

[Christophe Varoqui]

Le dimanche 07 mai 2006 à 17:01 +0300, Erez Zilber a écrit :
> Some more questions:
> 
>    1. I couldn't find the config file. Where is it located? Is there any
>       documentation about it?

The config file normal location is /etc/multipath.conf

>    2. How can I configure fancy naming for devices (instaed of using
>       something like /dev/mapper/3600c0ff00000000007c1d121c397f503) in
>       the config file?

Have a look at the templates provided with the upstream package.

>    3. How can I config the delay from the time that a device has failed
>       until the dm moves to the next active device? Again, I understand
>       that I should use the config file somehow.
> 
Ditto.

> I tried to run the following test: I created a multipath device with 2 
> physical devices (/dev/sda & /dev/sdb). I started running traffic on the 
> multipath device. All traffic ran through /dev/sda. Then, I disconnected 
> the iSCSI target that was represented by /dev/sda. After some time, the 
> traffic was directed to /dev/sdb. I stopped the traffic, disconnected 
> the iSCSI target that was represented by /dev/sdb and reconnected 
> /dev/sda. Now, if I run `multipath -l`, I see the following output:
> 
> 3600c0ff00000000007c1d121c397f503
> [size=10 GB][features=0][hwhandler=0]
> \_ round-robin 0 [prio=0][enabled]
>  \_ 0:0:0:0 sda 8:0   [failed][undef]
> \_ round-robin 0 [prio=0][enabled]
>  \_ 1:0:0:0 sdb 8:16  [failed][faulty]
> 
> /dev/sdb is dead and I'm ok with it. However, /dev/sda is alive. I was 
> able to run the following command:
> 
> dd if=/dev/sda of=/dev/null count=100000
> 
> However, if I run the following command:
> 
> dd if=/dev/mapper/3600c0ff00000000007c1d121c397f503 of=/dev/null 
> count=100000
> 
> This is what I get:
> 
> dd: reading `/dev/mapper/3600c0ff00000000007c1d121c397f503': 
> Input/output error
> 0+0 records in
> 0+0 records out
> 0 bytes (0 B) copied, 0.00067 seconds, 0.0 kB/s
> 
> Can't it recongnize that a device that has failed (/dev/sda) is back to 
> life?
> 
Is the daemon (multipathd) running ? The daemon takes care of path
revalidation.

Regards,
cvaroqui