[linux-lvm] Re: How big are PEs by default?
Joao Rechena
security at rechena.com
Tue Mar 11 06:23:01 UTC 2003
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 at rechena.com
http://www.rechena.com
================================
"Bow before me for I am root"
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