What a hassle!
I tested some today, and found that indeed, it takes some time before
changes are seen on the R/O disk. But if I do a sync after my database
backup (on the RW linux), then umount/mount pm the RO,
the changes are immediately visible. Why should I have to do a
detach/attach?
By the way, dasdview showed that the VTOC had been corrupted. (Thanks,
Peter) Strangely, SLES10R3 could still read/write the disk, but none of
the other machines could mount it. After DASDFMT, FDASD and mkfs, it's
working again from both versions. I'm still using ext2 because I'm
sceptical about using XFS, Isn't it a journaling filesystem?
Nice obituary on Dennis Ritchie on the NYTimes. Made me want to pull
out my dog-eared copy of K&R and read some of his prose. For me, he was
a bigger benefactor for the world than Steve Jobs.
Have a nice weekend, everybody.
Med vennlig hilsen
Roger Evans
Autodata Norge A/S
________________________________________________________________________
On Thu, 2011-10-13 at 13:12 +0200, Agblad Tore wrote:
> Well if you write only at specified times, to get away with this you have to:
>
> before a write: unmount , offline and detatch disks in read-only servers
> do your write in the write/right server :) hehe
> after write: link+online+mount
>
> then you should be safe, this is if properly done the SOMETHING you have to
> use, the simplest one you can get.
>
> Cordialement / Vriendelijke Groeten / Best Regards / Med Vänliga Hälsningar
> Tore Agblad
> ________________________________________________
> Tore Agblad
> System programmer, Volvo IT certified IT Architect
> Volvo Information Technology
> Infrastructure Mainframe Design & Development, Linux servers
> Dept 4352 DA1S
> SE-405 08, Gothenburg Sweden
> Telephone: +46-31-3233569
> E-mail: [email protected]
> http://www.volvo.com/volvoit/global/en-gb/
> ________________________________________
> From: Linux on 390 Port [[email protected]] On Behalf Of Roger Evans
> [[email protected]]
> Sent: Wednesday, October 12, 2011 10:43
> To: [email protected]
> Subject: Re: dasd_configure doesn't see partition 1 on RO disk
>
> Well - not 'any time' - as I only write to the disk at specific times.
> Maybe I should do a "sync" on the RW side and schedule a remount on the
> RO side afterwards.
>
> best regards/Med vennlig hilsen
>
> Roger Evans
>
> Systemkonsulent
>
>
> ________________________________________________________________________
>
>
>
> On Wed, 2011-10-12 at 10:15 +0200, Agblad Tore wrote:
>
> > The server that has it in rw mode can write new data at any time.
> > Thus reorganize datablocks inodes and whatever needed to fit the new files
> > into free space.
> > The other server may not be aware of this move of bytes on the disk.
> > So an IO error might happen, or maybe read-error, don't know which.
> >
> > _________________________________________________
> > Tore Agblad
> > System programmer, Volvo IT certified IT Architect
> > Volvo Information Technology
> > Infrastructure Mainframe Design & Development, Linux servers
> > Dept 4352 DA1S
> > SE-405 08, Gothenburg Sweden
> > Telephone: +46-31-3233569
> > E-mail: [email protected]
> > http://www.volvo.com/volvoit/global/en-gb/
> >
> >
> > -----Original Message-----
> > From: Linux on 390 Port [mailto:[email protected]] On Behalf Of Roger
> > Evans
> > Sent: den 12 oktober 2011 09:44
> > To: [email protected]
> > Subject: Re: dasd_configure doesn't see partition 1 on RO disk
> >
> > I've been using this scenario for database backups since we had the
> > discussion about shared VM disks on this thread about a year ago.
> > David made the point then that if you had a hipervisor that allowed it,
> > not making a disk dependent on one of the machines being up at all times
> > (as with NFS), had some advantages.. I also used Tore's suggestion to
> > stick to ext2 so nobody would try to replay a journal. .I use them
> > for database backups that I take each night, and for SLES10 (both SP1
> > and SP3) it works fine. IF the RW linux is down (usually because it
> > didn't come up again), caching won't be an issue.
> >
> > If the machine that 'owns' the database/disk is down, I can still see
> > the database, and can recover a copy on the machine that has RO access.
> > without having to go in and change the VM configuration. It's also easy
> > to
> > check to see that the backup went ok. and the recovery would work.
> >
> > I haven't tried sharing a disk between 2 SLES 11 machines yet, and
> > that's where I'm going with upgrades. If it doesn't work, it would be
> > nice to know. Why would the fact that one of the machines has the disk
> > mounted RW
> > keep the other(s) from seeing it at all?
> >
> > Best Regards/
> > Med vennlig hilsen
> >
> > Roger Evans
> >
> >
> >
> > ________________________________________________________________________
> >
> >
> >
> > On Tue, 2011-10-11 at 10:11 -0600, Mark Post wrote:
> >
> > > >>> On 10/11/2011 at 04:26 AM, Roger Evans <[email protected]> wrote:
> > > > I am trying to mount a disk R/O from two linux machines on one VM. One
> > > > of them is SLES10 where the disk is defined in zipl.conf. The other
> > > > is a new SLES11 ('CLPRODB2)..
> > > >
> > > > The disk is mounted RW on a SLES10sp3 machine.
> > >
> > > This is never a good idea. If you want to share a disk between z/VM
> > > guests, _all_ of them need to have it read only. None of them can have
> > > it read-write. There's too many layers of caching going on for it to
> > > work reliably, if at all.
> > >
> > > If you absolutely have to have access to a disk that is mounted
> > > read-write, use NFS to export it read only.
> > >
> > >
> > > Mark Post
> > >
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