[Linux-cluster] Export directory via gnbd

[Michael Will]

carlopmart at gmail.com wrote:

> Hi all,
>
>  Is it possible to export directorys via gnbd?? GNBD docs only 
> descrives how to export files or partitons ...
>
There is a difference between block-level and file-level export of storage.

block level:

Just like iSCSI would, GNBD does export one chunk of data without
knowing anything about the structure of what you write to it. The client can
use it as if it was a local disk (with some limitations), which means it can
read and write blocks of data. It could be mysql writing database data, 
or it
could be the OS writing a filesystem on it. The GNBD server does not know
or care.  NBD=network block device.

Two clients could access the same blockdevice read-write, but you would need
a network protocol that negotiates locking and caching so that the two 
separate
clients don't step over each others data. GFS is one for filesystems, 
mysql-cluster
implements the same for a relational database.

file-level:

Just like a NAS or an NFS-server, the server exports a filesystem to 
clients.
So instead of requesting read/write of blocks of data, the clients 
requesting
listing directories, locking, reading and writing to files. 

So to answer your question 'how do I export a directory via gnbd' you might
have to reword it with the above clarification. Instead of NBD you can use
NFS to export a directory to multiple clients, or GFS if you plan to 
export from
multiple machines to multiple clients.

Michael

-- 
Michael Will
Penguin Computing Corp.
Sales Engineer
415-954-2822
415-954-2899 fx
mwill at penguincomputing.com