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Re: [linux-lvm] Mirrored LV



Just to answer some questions:

You can use just 2 disks to create a mirror and a disk log:
prompt> lvcreate --alloc anywhere -m1 -L 500M -n my_lv my_vg

I wish the allocation policy 'normal' (which is the default) would also do this... but instead you must choose a looser allocation policy to get what you want.

The reason that you want the disk-based log is to prevent all the extra work when you machine comes up.

The reason that LVM wants a separate disk for the log is so the head on the storage device doesn't need to go ping-ponging around the device. (The log is touched for almost every write.) So, its a performance thing... and possibly a not-wear-out-your-hardware thing too.

It won't matter if the master disk with the log dies. Your mirror will simply become a linear device composed of the last remaining disk anyway.

 brassow


On Sep 19, 2008, at 5:01 PM, Koen Vermeer wrote:

Op vrijdag 19-09-2008 om 10:31 uur [tijdzone -0700], schreef
malahal us ibm com:
It needs it own PV. Create an extra partition on your master disk and
add the PV tou the volume group.  Then run lvcreate again with out
corelog option. By default the command would create a disklog. You can
also specify where you want your log.

OK, did that! I guess I need one additional partition for each volume
group, then.

Now, what happens if the master disk (which includes the log) dies?
Won't LVM complain that it cannot find the log? I'm not saying I expect
it too, but with this stuff I guess it's better to be safe than sorry!

Best,
Koen

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