Linux sharing a JBOD- paul’s question

23 05 2008

“Question about multiple servers accessing same disks through a SAN switch

I’m trying to set up a Linux system for server failover where two servers (with SAS HBA) are accessing the same set of disks (jbod) through a SAN switch. First – will this work? If so, what software do I need to run on the servers to keep the two servers from stepping on each other? Do I need multipath support?”

It depends. A JBOD does not do any RAID management- it leaves that to the servers. If you have two servers trying to operate on the same disks, they have to be using a clustering operating system to avoid overwriting themselves. Linux is probably able to do that, and I know Windows has a cluster edition, but it’s certainly not the simplest way to get servers sharing data.

This brings me to my first question: what are you trying to do? Do you want them to run the same application so if one fails, the other will pick up the slack without losing anything? Or are you trying to process the same data twice as fast by using two server “heads”?

Secondly, when you say “SAN switch”, do you mean fibre channel switches? If you have SAS HBAs, those can not plug into an FC network.

Thirdly, multipath support usually implies allowing a server to see a single LUN through multiple fabrics. If you have more than one path between every server and drive, multipathing software would indeed be suggested.

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2 responses

23 05 2008
Paul

Thanks for the folow-up. What I am trying to do is simply fail-over a server. I’m using IBRIX clustering software – however when I try to do discovery of physical volumes all hell breaks loose with disk I/O errors at the server level.

Second, I misinformed. I am using a SAS switch with zoning control to control access to the disk enclosures and disks from the two servers.

Thanks again.

24 05 2008
Open Systems Guy

Ah! I understand now :)

It sounds like both servers are trying to be a primary disk owner on the same disks, and this will definitely cause errors. Unfortunately, I don’t know IBRIX at all, and I have no experience clustering servers. It looks like what you need to do is configure your software so it knows both nodes are going to be accessing the same disks, and makes sure they don’t step on each others feet. IBRIX should have some sort of guide for this. They may also need to know how you’re doing your zoning on the switch.

Once you have that set up, if you want to try to increase your availability you could look into multipathing, but you should ensure that you use a setup that’s been tested by IBRIX. They might have specific needs for multipath drivers or the like.

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