[7822] in linux-scsi channel archive
Re: SCSI Sync Problem.
daemon@ATHENA.MIT.EDU (Burn Alting)
Thu Jan 13 10:37:23 2000
Date: Thu, 13 Jan 2000 12:13:12 +1100 (EST)
From: Burn Alting <burn@comptex.com.au>
Message-Id: <200001130113.MAA16673@stf.comptex.com.au>
To: linux-scsi@vger.rutgers.edu
>
> On Tue, Jan 11, 2000 at 09:48:16AM +0530, Krishna Sreehasam wrote:
> > hi,
> > I have a problem with syncing of data on to the SCSi disk. I have a
> > SCSI disk pack connected to two machines acting as a shared disk. The
> > problem is if I write data from one machine and then try to read it from
> > the other, the data is not visible. I mounted the partition on machine1
> > and then tried to write some data. It was visible then. Then, I unmounted
> > it and mounted the same partition from the machine2. The data which
> > I wrote was not visible there. I think it is a syncing problem. Any
> > ideas,explanations,suggestionsans solutions are extremely welcome. please
> > do mail me if you need any extra information.
>
> On Wed, 12 Jan 2000 21:45:09 +0100, Kurt Garloff wrote:
>
> A setup with two hosts sharing a disk is possible, but be aware of the fact,
> that both kernels buffer the data, which they read from disk or which they
> want to write to the disk. One kernel can not know, that the other changed
> a file.
> This is no problem, if you don't have the same partition mounted on both
> computers.
> If you want to do that, you can mount it ro on both boxes. That won't give
> any problems, as one can not change the data behind the other one's back.
>
> If you want to write to a shared partition, things get really complicated.
> You can mount a partition rw on one box and ro on another one. The box,
> which has the partition mounted ro might crash, but you won't corrupt your
> filesystem, at least. This will most possibly happen, if you mount rw on
> more than one host.
Given you want to 'share' the filesystem quite often and the mount/umount
senario is not sufficient, then you should look at University of Minnesota's
GFS filesystem - www.globalfilesystem.org - which will allow you to share
the disk (and it's filesystem) between your two hosts. Although it is in
an 'Alpha/Pre-Beta' status, it could be the more medium to longer term solution
for you.
Burn Alting 1A/7 Lloyds Avenue, Carlingford NSW 2118 Australia
Comptex Pty Limited Ph/Fx: +61 2 9872 6394 / +61 2 9872 3765
burn@comptex.com.au
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