Some questions after starting to use 1.1-rc1
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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 $x}'and I find that striped LVM takes 50% longer.
which stripe size did you use?
I don't think I specified -- so "the default" ?
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Were the PVs on non-saturated pathes?
What are "non-saturated pathes" ?
There were two PVs, each on an otherwise unused IDE bus.
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Did you compare LVM1 Raid0 to MD Raid0 on the very same hardware?
Yes.
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2) When I tried to extend the striped partition, it failed when it used up the first two PVs, and will not start the next two. Ideas ?
That's a LVM1 constraint which will disapear with LVM2.
:-(
Is there an introductory document on device-mapper ?
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No need to vgexport to test it.
Hmmm ...
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Just stop one PV as you did
stop the RAID device while it's in use by LVM ?
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b) should it be possible to export a VG if there is a PV of that VG
which
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is still exported ?
?
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5) is there some utility to display the contents of VGDA on disk,
/etc/lvm*, etc; show where the first PE is in a PV, etc ?Run "pvdata -a" on the particular PV.
Where does it say "PE 0 starts at byte offset <n> of the device" ?
Hi Piete.
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1) I've been comparing the speed of LVM over RAID0 with striped LVM, using:
perl -e '$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.
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Were the PVs on non-saturated pathes?
What are "non-saturated pathes" ?
Those with enough (free) bandwidth.
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There were two PVs, each on an otherwise unused IDE bus.
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Did you compare LVM1 Raid0 to MD Raid0 on the very same hardware?
Yes.
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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.
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No need to vgexport to test it.
Hmmm ...
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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.
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b) should it be possible to export a VG if there is a PV of that VG
which
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is still exported ?
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?
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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.
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