[Linux-cluster] Sharing disk using gnbd

[Bowie Bailey]

Mark Wormgoor wrote:
> Hi,
> 
> I have a small network with 3 machines. All machines are FC5 as of
> yesterday. One machine is a server and has most of my storage. I'm
> currently sharing the disks using NFS, but am researching better ways
> of sharing my disks. My main reason for doing this is that I would
> like Posix semantics, but better performance over NFS would be a nice
> benefit. 
> 
> I think my main options are gnbd (GFS), iscsi and ata-over-ethernet.
> Since GFS is best supported in Fedora, that was my first attempt.
> However, when going through the docs, I noticed that I could not mount
> the disk on the server itsself.
> 1. If you use GFS on the disk and mount it like that on the server,
> you have to share it using gnbd with nocache, which is a huge
> performance hit. 
> 2. According to the gnbd docs, you should never import the disks on
> the machine they are exported on, so that's out as well.
> Can this be true? Is gnbd unusable if you want to use the disk on the
> server? On the other hand, GFS is a bit overkill, since I don't need
> the clustering; I just want to share my disk.
> 
> However, for aoe and iscsi, I think there is no way of sharing the
> file system between multiple systems, which would make them unusable.
> Besides, I could not find rpms for aoe, and for iscsi I could only
> find the server rpm, not the client.

You DO need the clustering.  That is what you are doing with
GNBD/iSCSI/AoE.  You are allowing multiple computers to read/write
directly to the storage media.  This requires GFS and a cluster to
manage access and prevent the storage from becoming corrupted.  With
NFS, the clients only access the storage through the NFS server, so do
not need this.

AoE and iSCSI can be natively shared with as many computers as you can
connect up to the storage network.  I don't know where you can find
the iSCSI drivers, but for AoE, you can get them from
http://www.coraid.com/support/linux/.  It's not an rpm, but a small,
easily compiled tarball.  There may be an rpm version somewhere, but
I've always just compiled it myself.

I can't comment on the limitations of GNBD.  I've never used it
myself, so I'm not sure.

-- 
Bowie