Re: [linux-lvm] LVM and devices

[Heinz Mauelshagen <mauelsha ez-darmstadt telekom de>]

> 
> Heinz writes:
> > > I haven't had a chance to
> > > look yet).  For that matter, LVM shouldn't be tied to the /dev names of
> > > anything, since you could just start traversing the available devices,
> > > find a list of UUIDs that make up a VG, and not have to worry about the
> > > /dev names of anything (nor even store them anywhere).
> > 
> > Actually, it depends on /dev namespace today.
> > 
> > But the sole reason for this is perforrmance.
> > 
> > We could simply throw that dependency away, if we go devfs or
> > could live with performance impacts without devfs.
> 
> It shouldn't be a big change to have LVM not STORE the device names in
> the VGDA,

It doesn't use a stored devices name in the PV part of the VGDA today.
The device name is inserted at PV read time (see pv_read()).

> and something like a pvscan is done at boot-time (after the LVM
> module is loaded, if a module) to determine PV -> /dev mapping.  The LVM
> kernel code would still use the device name/major+minor in memory to
> access the devices, so there should be no performance impact outside a
> small amount of scanning at boot time or when a new VG is imported.
> 

What i meant with performance impact is the longer time to scan large
/dev configurations in user space (vgscan, pvscan and friends).

Regards,
Heinz
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Systemmanagement CS-TS                           T-Nova
                                                 Entwicklungszentrum Darmstadt
Heinz Mauelshagen                                Otto-Roehm-Strasse 71c
Senior Systems Engineer                          Postfach 10 05 41
                                                 64205 Darmstadt
mge ez-darmstadt telekom de                      Germany
                                                 +49 6151 886-425
                                                          FAX-386
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