Re: Re: is it possible to access

Hi Stefan,
> You can't.  The enbd server's kernel and file system cache have not been
> traversed when the enbd client writes into the device (partition,
> whatever) underneath it.
Yes, completely right - that is not related to enbd at all and a relly general trap, users fall into.
You cannot mount blockdevices containing ordinary filesystems from more than one location - period.
Mounting it a second time results in severe inconsistencies.

There are special cluster filesystems (e.g. Veritas Storage Foundation, Oracle OCFS,Polyserve... ) which adress this issue - e.g if
you have multi-node clusters (like Oracle RAC) which share a single storage device.

regards
Roland


----- Original Message ----- 
From: "Peter T. Breuer" <[email protected]>
To: <[email protected]>
Sent: Wednesday, February 09, 2005 4:28 PM
Subject: [ENBD] Re: is it possible to access


> Stefan Pielicke <[email protected]> wrote:
> > Hi,
> >
> > On Tuesday 01 February 2005 16:42, Peter T. Breuer wrote:
> > > Why not simply put the enbd servers ON the clients? Then you have the
> > > enbd clients on your server, all RAID1-ed together into a device which
> > > includes whatever you are writing to on your server. Then all writes to
> > > it automatically go out to your "clients".
> >
> > ok, I've installed enbd like you said and it works very nice :)
> > Only one problem left, every time the enbd-client writes something on the
> > device I have to remount the partition on the enbd-server to see the changes.
> > How is it possible to see the changes immediatly (i.e. without remounting)?
>
> You can't.  The enbd server's kernel and file system cache have not been
> traversed when the enbd client writes into the device (partition,
> whatever) underneath it.
>
> This is the same as writing directly into a disk while the FS on the
> disk is mounted.  The result will be at best oblivion and more probably
> death and destruction, people turned into pillars of salt, and much
> wailing and gnashing of teeth.
>
> If you want the enbd servers (your clients) to see the changes made on
> the enbd client in the FS, then you will have to export the FS in
> question from the enbd client via nfs. Or you could use a distributed
> FS (eg. gfs). Tell me how if you do it.
>
> It's like having a disk accessed by two machines/kernels.
>
>
>
>
> Peter
>
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