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Re: [Linux-cluster] Samba Technical thread



Christopher R. Hertel wrote:

On Tue, Dec 07, 2004 at 03:29:32PM +0800, David Teigland wrote:
:

3. POSIX semantics
  GFS semantics aim to copy those of a local fs exactly, while others
  like NFS don't, although there's nothing precluding that (NFS4 can
  be close if not exact).


Question on this. Is there any interest in clustered block media?

Eg., what if five systems all had access to the same chunk of (virtual) disk via iSCSI. Is there a way that one of those five could create an
EXT3 filesystem on that raw block-space such that all of the five clustered systems would see an EXT3 partition (and be able to use it concurrently)?
No (well not for a writable filesystem). You still need a cluster filesystem so you don't trash the filesystem. I believe that work is underway for a cluster raid to run gfs on top of. This would be good for people without shared storage hardware but still want to use GFS.

Oh... and a side-comment. CIFS tries, and gets fairly close, to copy lovsl FS semantics. The problem is that those semantics are DOS, OS/2, and NTFS semantics. The protocol has support for all of these, and there are some folks who have tried to add Unix semantics as well.
I did the initial implementation of the Unix semantics in the smbfs driver. POSIX semantics just aren't possible over CIFS. Unlinking an open file for example. I tried for weeks to implement that in smbfs and samba. Windows does not have such a concept so it is very difficult to make it work over CIFS. This means that programs that do stupid NFS locking workarounds (like gconfd) won't run with CIFS mounted home directories.

John.


Chris -)-----




--
John Newbigin
Computer Systems Officer
Faculty of Information and Communication Technologies
Swinburne University of Technology
Melbourne, Australia
http://www.it.swin.edu.au/staff/jnewbigin


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