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[Linux-cluster] Re: [linux-lvm] Distributed LVM/filesystem/storage



Jan-Benedict Glaw wrote:
On Fri, 2008-05-30 09:03:35 +0100, Gerrard Geldenhuis <Gerrard Geldenhuis datacash com> wrote:
On Behalf Of Jan-Benedict Glaw
I'm just thinking about using my friend's overly empty harddisks for a
common large filesystem by merging them all together into a single,
large storage pool accessible by everybody.
[...]
It would be nice to see if anybody of you did the same before (merging
the free space from a lot computers into one commonly used large
filesystem), if it was successful and what techniques
(LVM/NBD/DM/MD/iSCSI/Tahoe/Freenet/Other P2P/...) you used to get there,
and how well that worked out in the end.
Maybe have a look at GFS.

GFS (or GFS2 fwiw) imposes a single, shared storage as its backend. At
least I get that from reading the documentation. This would result in
merging all the single disks via NBD/LVM to one machine first and
export that merged volume back via NBD/iSCSI to the nodes. In case the
actual data is local to a client, it would still be first send to the
central machine (running LVM) and loaded back from there. Not as
distributed as I hoped, or are there other configuration possibilities
to not go that route?

GFS is certainly developed and well tuned in a SAN environment where the shared storage(s) and cluster nodes reside on the very same fibre channel switch network. However, with its symmetric architecture, nothing can prevent it running on top of a group of iscsi disks (with GFS node as initiator), as long as each node can see and access these disks. It doesn't care where the iscsi targets live, nor how many there are. Of course, whether it can perform well in this environment is another story. In short, the notion that GFS requires all disks to be merged into one machine first and then export the merged volume back to the GFS node is *not* correct.

I actually have a 4-nodes cluster in my house. Two nodes running Linux iscsi initiators that have a 2-node GFS cluster setup. Another two nodes running a special version of free-BSD as iscsi targets, each directly exports their local disks to the GFS nodes. I have not put too much IO loads on the GFS nodes though (since the cluster is mostly used to study storage block allocation issues - not for real data and/or application).

cc linxu-cluster

-- Wendy





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