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how to practise multipathing?

 
iinfi1
Super Advisor

how to practise multipathing?

hi all
all these days i used to use openfiler to practice clustering on linux and windows ... those days i used to create iSCSI targets using openfiler and map it to the linux or windows boxes using iscsi initiator!!!
now my client setup has a SAN box from where the LUN is presented to the servers and we do not have to use the iscsi initiator to the map the storage.
is there anyway i can use openfiler to practice this scenario and practice multipathing in my laptop at home?
thanks..
4 REPLIES
dirk dierickx
Honored Contributor

Re: how to practise multipathing?

i don't know openfilter, but afaik it isn't included by default on linux. dm-multipath is however and it is the recommended method of providing multipath functionality. it works on any storage connection protocol linux can use.

another way is to use the multipath capabilities of some fc-cards, for this you will need to install vendor drivers that offer those functionalities.

we use dm-multipath.

to emulate this in your laptop, i'm not sure how this is done. what you should do is add 2 virtual drives that point to the same disk device, never tried this myself.
AnthonySN
Respected Contributor

Re: how to practise multipathing?

go thru the below link for understanding native multipathing from redhat

http://www.redhat.com/docs/manuals/csgfs/browse/4.6/DM_Multipath/index.html
Matti_Kurkela
Honored Contributor

Re: how to practise multipathing?

Yes, it's possible to practice multipathing using iSCSI.

Pay attention to the iSCSI timeout parameters in the initiator configuration: in RedHat Enterprise Linux, the default iSCSI timeout parameters are 120 and 20 seconds, which means the iSCSI subsystem will keep trying one path for quite a while before the multipath subsystem is even informed that a problem exists.

In a multipath configuration, you'll actually want the bottom layer (iSCSI in this case) to report a failure pretty soon (about 5-10 s), so the multipath layer can retry the request using the other path.
In Linux, adjust the timeouts in /etc/iscsi/iscsid.conf.

When testing Linux dm-multipathing using iSCSI, set the default "path_grouping_policy" to "failover" in /etc/multipath.conf. This makes the multipath use the paths in explicit active/passive fashion, making it easier to see what is happening. Once you see that the "failover" policy works, you can try other modes.

You might want to set up your network so that you can access the openfiler through two NICs (or VLANs, if only one NIC is available in your client system). This would allow you to easily simulate a break in one or both paths by switching off the appropriate network interface(s) using ifdown/ifup.

Note:
In a RedHat Enterprose Clustering and Storage Management course (RH436), various cluster-related technologies are practiced in several lab sessions. When I sat the course, each student had access to one physical computer, which included an iSCSI target on the host system, and multiple Xen virtual machines as guests. There was a pre-arranged Xen virtual network configuration with multiple virtual network segments, which made it easy to practice multipathing.

I guess you're trying to set up something similar?

MK
MK
iinfi1
Super Advisor

Re: how to practise multipathing?

thank you all ..
i think wat Matti explained will apply in my case .. i will try what u v jus explained.

thanks again