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

gordan at bobich.net gordan at bobich.net
Fri Jan 25 10:25:17 UTC 2008



On Fri, 25 Jan 2008, Ferenc Wagner wrote:

> "isplist at logicore.net" <isplist at logicore.net> writes:
>
>> What I was hoping to do with the partitions was to give each blade
>> it's own boot and scratch space, then allow each blade to have/use
>> shared storage for the rest. I was hoping to boot the machines from
>> FC or perhaps PXE.
>
> I'm doing something like that on a BladeCenter.  The (diskless) blades
> boot using PXE/DHCP/TFTP from a central server.  They can see over FC
> two storage partitions.  On the first, there is an LVM2 VG with a
> single LV for the root filesystem of each blade.  On the other there's
> GFS which they all mount after booting up.

What about the overhead of managing unshared local roots? Nobody seems to 
account for that, and IMO, it's signifficant.

> This setup is simple, but lacks the shared root of OpenSharedroot.  I
> decided to go with the simpler design with more wasted space, because
> the root volumes aren't particularly big, only a few GBs each.
> Another refinement could be creating LVM snapshots of a common "image"
> root LV for each booting server, which would again cut down on disk
> space for the price of added complexity.
>
> In another case, building several bigger but volatile clusters, I went
> for a shared read-only NFS root with some symlinks into tmpfs's for
> the files that had to be writeable.  There was no SAN in that picture
> at all, a read-write NFS share was enough, since locking wasn't an
> issue.

Indeed, NFS can be almost as good as GFS if you don't need fully 
operational locking. There are also scenarios where it's faster than GFS.

Gordan




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