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Re: [Linux-cluster] SSI, Virtual Servers, ShareRoot, Etc



What I badly need right now is a shared root style system. Perhaps where all
nodes boot from the FC SAN using their HBA's and all have access to GFS
storage all around the network.

There are various reasons I would like to do this but one of them also
includes trying to save on power. Say I took 32 machines and was able to get
them all booting off the network without drives, then I could use a 12 drive
FC chassis as the boot server.

You could do that, but see the comment further down about needing local disks for at least scratch space. It ultimately depends on your application.

What I had worked on last year was partitioning one of these chassis into 32
partitions, one for each system but I think there is a better way and, maybe
even gaining some benefits.

Indeed. That sounds rather like you were using a SAN just for the sake of using a SAN, and taking all the disadvantages without any of the advantages.

The problem with that was that partitions were
fixed and inaccessible as individual partitions once formatted on the storage
chassis. A shared root system would be better because then I don't have to
have fixed partitions, just files. Then, each node would have it's storage
over other storage chassis on the network. This is what I would like to
achieve, so far, without success.

Not sure what you mean there, the last two sentences didn't quite parse. Can you please elaborate?

maybe before going right into SSI which seems to be quite an effort to
get running, you might want to think about "cloning" system images by
using any kind of volume manager and copy on write volumes. lvm2 for
instance does support this.

That would make things more complicated to set up AND more complicated to maintain and keep in sync afterwards. SSI isn't hard to set up. Follow the OSR howto and you'll have it up and running in no time.

The only thing I'd do differently than the howto is that I wouldn't unshare the whole of /var, but only /var/log, /var/lock and /var/run (off the top of my head. It's useful to keep things like /var/cache shared. But that's all fairly minor stuff. The howto will get you up and running.

you basically create one master image, do all the basic configuration,
such as routes, connection to your ldap server, whatever, and then just
make snapshots of that image for every node / vm you want to create.
you can make those snapshots writeable, which basically creates a
copy-on-write datafile.

Or you could just create a shared root volume after you've set up the first one, and get everything talking to that. The only minor downside is that you still need a local disk for the initrd base root (otherwise you waste about 120MB of RAM), swap and /tmp, plus any other major file systems you want unshared for performance (e.g. replicated DB copies that are replicated outside of the clustering framework).

The major upshot of SSI is that you only need to manage one file system, which means you can both use smaller disks in the nodes, and save yourself the hassle of keeping all the packages/libraries/configs in sync.

Gordan


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