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[linux-lvm] Re: How big are PEs by default?



Patrick Caulfield writes:

On Tue, Mar 11, 2003 at 11:22:20AM +0000, Paul Furness wrote:
Hi.

I'm trying to get LVM 1.0.7 going on our new production server. I've
never used LVM before, but based on reccommendations and looking at what
it can do, it looks like exactly what I need.


For the reccord, it's a SMP Xeon system, running RedHat 7.3 plus current
RH patches.


I am confused about the defualt setting for Physical Extents when you
run vgcreate on a new PV.


Looking through the man page for vgcreate is says this:

-s, --physicalextentsize PhysicalExtentSize[kKmMgGtT]
Sets the physical extent size on physical volumes
of this volume group. ................. The default
of 32 MB allows LV sizes of ~2TB because as many as
~64k extents are supported per LV.


A bit later, under "Examples." it says this:

To create a volume group named test_vg using physical vol-
umes /dev/hdk1, /dev/hdl1, and /dev/hdm1 with default
physical extent size of 4MB:


vgcreate test_vg /dev/sd[k-m]1


So what is the default? 4M or 32M? Or something else? Or should I simply forget about the default and pick a number?

The default is 32MB, the example has not been updated. It used to be 4MB but
limiting LVs to 256MB by default soon became a problem for people.



Finally, is there any documentation that's more detailed than the HOWTO,
and explains a bit more about the theory of LVM - what happens when you
change the size of existing file systems, and so on? The HowTo is ok
(although not all that great if you've never patched a kernel before),
but necessarily brief. :)

You could try to read the documentation of HP LVM, wich is a little more detailed, but be carefull, there are some commands that are diferent.
I dont have the link here with me now but I can search later on.


Regards


rech
--
Joao Rechena
mailto:security rechena com
http://www.rechena.com
================================
"Bow before me for I am root"




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