Hi Piete.
On Thu, Apr 25, 2002 at 10:33:07PM +0100, Piete Brooks wrote:
> >> 1) I've been comparing the speed of LVM over RAID0 with striped LVM, using:
> >> perl -e '$n=1900;$x="X"x(1024*1024);foreach $i(1..$n){print $x}'
> >> and I find that striped LVM takes 50% longer.
> > which stripe size did you use?
>
> I don't think I specified -- so "the default" ?
That's 16k then.
>
> > Were the PVs on non-saturated pathes?
>
> What are "non-saturated pathes" ?
Those with enough (free) bandwidth.
>
> There were two PVs, each on an otherwise unused IDE bus.
>
> > Did you compare LVM1 Raid0 to MD Raid0 on the very same hardware?
>
> Yes.
>
> >> 2) When I tried to extend the striped partition, it failed when it used up
> >> the first two PVs, and will not start the next two. Ideas ?
> > That's a LVM1 constraint which will disapear with LVM2.
>
> :-(
>
> Is there an introductory document on device-mapper ?
Download the device-mapper code from
ftp://ftp.sistina.com/pub/LVM2/device-mapper/
and read the INTRO file.
>
> > No need to vgexport to test it.
>
> Hmmm ...
>
> > Just stop one PV as you did
>
> stop the RAID device while it's in use by LVM ?
Well, if you do this while the extents on it are actively used, Linux
will soon start to expose io errors. If you deactivate/activate the VG
then it should still come up with "vgchange -qn".
If you want to avoid the io errors in your test case, deactivate the VG,
deactivate the PV and "vgchange -qn" the VG again.
>
> >> b) should it be possible to export a VG if there is a PV of that VG
> which
> >> is still exported ?
>
> ?
>
> >> 5) is there some utility to display the contents of VGDA on disk, /etc/lvm*,
> >> etc; show where the first PE is in a PV, etc ?
> > Run "pvdata -a" on the particular PV.
>
> Where does it say "PE 0 starts at byte offset <n> of the device" ?
Sorry, my fault.
Use "pvdata -PP" and calculate "pe_on_disk.base" + "pe_on_disk_size",
which gives you the offset of the first PE in bytes.
Or run "pvdisplay -v" on the PV, which lists the offsets for all PEs
in sectors of 512 byte.
>
>
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--
Regards,
Heinz -- The LVM Guy --
*** Software bugs are stupid.
Nevertheless it needs not so stupid people to solve them ***
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Heinz Mauelshagen Sistina Software Inc.
Senior Consultant/Developer Am Sonnenhang 11
56242 Marienrachdorf
Germany
Mauelshagen@Sistina.com +49 2626 141200
FAX 924446
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