[linux-lvm] Why vgscan not in kernel?
Heinz J. Mauelshagen
Mauelshagen at sistina.com
Mon Jun 25 23:13:08 UTC 2001
On Mon, Jun 25, 2001 at 02:54:52PM +0200, josv at osp.nl wrote:
> If the VG scan process is in the kernel, that means that it
> will *always* be executed (unless there is a kernel command
> line option to disable it).
> The issue then is that the VGSCAN in the kernel should be
> *completely* resistant against every possible data corruption
> and should be able to recover from it gracefully. This is not
> as easy as it looks.
that's true. We'll try to provide that kind of redundancy/resistancy in a
post 1.0 release by having
- checksums on all VGDA structures
- two copies of the VGDA and
- transaction oriented updates to VGDA contents
This should give us enough power to recover from a lot of potential cases.
BTW: there's will be a flag to switch init time activation per VG on and off.
Heinz -- The LVM Guy --
> With VG scan in a separate executable, it is easier to prevent
> it from executing...
> And thus it came to pass that Dirk Heinrichs wrote:
> (on Mon, Jun 25, 2001 at 02:52:00PM +0200 to be exact)
> > Steven Lembark wrote:
> > >
> > > >> upon boot, SCSI and IDE drivers check harddrives attached to the device
> > > >> for partitions. Wouldn't it be better to have similar functionality
> > > >> (scanning for VG's) for LVM in the kernel, instead of using a userland
> > > >> command?
> > >
> > > It is rather dangerous unless you have a separate kernel w/o LVM or
> > > a boot option (e.g., -lm) that allows booting with LVM turned off.
> > > Otherwise you can easily end up unable to reboot with a corrupt LVM
> > > system.
> > I don't get the point here. Why is it dangerous to move the VG scan from
> > vgscan into the kernel module? Why should this corrupt LVM? Can you
> > explain this in more detail?
> > Bye...
> > Dirk
> > --
> > Dirk Heinrichs | Tel: +49 (0)241 413 260
> > Configuration Manager | Fax: +49 (0)241 413 2640
> > QIS Systemhaus GmbH | Mail: dheinrichs at qis-systemhaus.de
> > Jülicher Str. 338b | Web: http://www.qis-systemhaus.de
> > D-52070 Aachen | ICQ#: 110037733
> > _______________________________________________
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> > linux-lvm at sistina.com
> > http://lists.sistina.com/mailman/listinfo/linux-lvm
> > read the LVM HOW-TO at http://www.sistina.com/lvm/Pages/howto.html
> With all the things you are losing,
> You might as well resign yourself,
> And try and make a change...
> linux-lvm mailing list
> linux-lvm at sistina.com
> read the LVM HOW-TO at http://www.sistina.com/lvm/Pages/howto.html
*** Software bugs are stupid.
Nevertheless it needs not so stupid people to solve them ***
Heinz Mauelshagen Sistina Software Inc.
Senior Consultant/Developer Am Sonnenhang 11
Mauelshagen at Sistina.com +49 2626 141200
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