[linux-lvm] How big are PEs by default?
Patrick Caulfield
caulfield at sistina.com
Tue Mar 11 05:32:02 UTC 2003
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. :)
Not that I know of. But if you want to know what a filesystem does when it's
extended then you need filesystem documentation, not LVM documentation.
--
patrick
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