[Linux-cluster] Starter Cluster / GFS

Gordan Bobic gordan at bobich.net
Fri Nov 19 08:32:48 UTC 2010

Nicolas Ross wrote:
> 1. Raid sets
> So, I made up a 2-node cluster for the moment. I was able to bring up 
> the cluster and make a GFS file system, in fact 2. We've made some test 
> with different strategy of raid. Our first idea for the gfs was to use 5 
> 1tb disks in raid 5. With that I got a 4 tb fs. It has been suggested 
> previously that might not be a good idea. Our controler don't support 
> directly raid 10 wich seems to be the consensus of a better setup. We 
> will be making the 0 part on linux.
> I made 2 raid 1 sets of 1tb (2 disks) on our raid enclosure, and added 
> them to a single vg. I created a lv on top of that, so I yield with a 2 
> tb fs. We don't plan on using striping on the lv (-i2) because of the 
> overhead if we add more space we will need to add 2 sets of raid1. So we 
> plan on making a "starter" gfs with those 2 sets (2tb total). It's 
> nearly double the 1.1 tb we have now, so we'll start with that.
> Now, we made some write test with dd, and judging by the disk activity, 
> all data was writen to the first disk (pair of) of the vg, and never the 
> second one. I assume that once the first disk is full, it'll start 
> writing to the 2nd one. In the long term, I don't beleive it'll be a 
> problem, but I'd prefer if the data was written alternativly on both 
> disks without using stripes. Is that possible ? I looked at the --alloc 
> option to the vgcreate, but it doesn't seem to be that.

Is this the storage you are sharing between the nodes? If so, how 
exactly are you doing it?

Also, you do realize that you don't have to use LVM at all? It is 
entirely optional.

> 2. Network setup.
> All our new servers have 3 nics, one being dedicated on to the 
> mamagement module. I will be using the first one to make a private 
> network that will be serving my services. In my new setup real routable 
> ips will terminated at the router and will be nated to the private ones 
> for eventual load-balancing. I will be using the second network on a 
> different vlan and subnet for cluster communications. The management 
> modules will be on that same vlan. So is this a good setup ? Should I be 
> doing something differently ?

In theory, your cluster/storage interface should be the same interface 
you access the fencing devices over. As long as you stick to that, it 
should be OK.

> 3. Deadlocks
> I found a small c program for testing the locks/s that is possible on a 
> file accessed similtunously on many nodes. (It's ping_pong, some fo you 
> might have used it). So, one of the parameters of that program is the 
> number of nodes using that file +1. On one test, I used 2 in stead of 3 
> on one of the node. Both profram on both nodes seemed stuck, not 
> killable, not even -9. So I must assume that they were in some kind of 
> deadlock. dlm_tool deadlock_check didn't show anything, and I can't make 
> heads or tails from gfs2_tool lockdump or what to do with it. I was 
> forced to reboot (forcebly) one of the node. Most likely on my 
> production environement we won't arrive to that situation. But I want to 
> know what happed and what to do to prevent it or stop that kind of lock.

What version of RHEL are you using? Early versions of RHEL5 had GFS2 
lock-up issues like you're describing. IIRC, GFS2 was only considered 
stable from around RHEL 5.5 (technology-preview-only in earlier versions 
of RHEL). Try with GFS1, it's a lot more mature.


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