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

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

[Paul Furness]

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?

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. :)


Thanks.

Paul.




-- 
Paul Furness

Systems Manager
Visual Information Lab
Mitsubsihi Electric ITE BV
Guildford, UK

Steepness is an illusion caused by flat things leaning over.

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

[Patrick Caulfield]

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

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

[Joao Rechena]

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" 

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

[Urs Thuermann]

Patrick Caulfield <caulfield@sistina.com> writes:

> 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.

Just a typo, but with a PE size of 4MB the limit is 256GB, not 256MB.


urs

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

[Patrick Caulfield]

On Thu, Mar 13, 2003 at 01:25:57PM +0100, Urs Thuermann wrote:
> Patrick Caulfield <caulfield@sistina.com> writes:
> 
> > 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.
> 
> Just a typo, but with a PE size of 4MB the limit is 256GB, not 256MB.

Arg!. Just showing my age again :(

Thanks


patrick

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

[Aaron Brock]

> 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. :)
>
Suse put out a white paper that may offer a little more detailed explanation
of LVM. It's available at:
http://www.suse.com/en/business/certifications/certified_software/oracle/doc
s/lvm_whitepaper.pdf


Aaron M. Brock

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

[hcalzaretta]

3590


-----Original Message-----
From: Aaron Brock [mailto:brock@ohiou.edu] 
Sent: Tuesday, March 11, 2003 9:52 AM
To: linux-lvm@sistina.com
Subject: Re: [linux-lvm] How big are PEs by default?


> 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. :)
>
Suse put out a white paper that may offer a little more detailed explanation
of LVM. It's available at:
http://www.suse.com/en/business/certifications/certified_software/oracle/doc
s/lvm_whitepaper.pdf


Aaron M. Brock


_______________________________________________
linux-lvm mailing list
linux-lvm@sistina.com http://lists.sistina.com/mailman/listinfo/linux-lvm
read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/

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

[Sharad Tiwari]

4MB is what I know ..

> >> 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. :)
> >>
> >Suse put out a white paper that may offer a little more detailed
> >explanation
> >of LVM. It's available at:
>
>http://www.suse.com/en/business/certifications/certified_software/oracl
e/
> >doc
> >s/lvm_whitepaper.pdf
> >
> >
> >Aaron M. Brock
> >
> >
> >_______________________________________________
> >linux-lvm mailing list
> >linux-lvm@sistina.com
http://lists.sistina.com/mailman/listinfo/linux-lvm
> >read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
> >
> >_______________________________________________
> >linux-lvm mailing list
> >linux-lvm@sistina.com
> >http://lists.sistina.com/mailman/listinfo/linux-lvm
> >read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/

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

[Patrick Caulfield]

On Tue, Apr 15, 2003 at 10:47:18AM +0530, Sharad Tiwari wrote:
> 4MB is what I know ..

They were until 1.0.6

Now they are 32MB
-- 

patrick