[linux-lvm] lvm config on disk?

Heinz J . Mauelshagen mauelshagen at sistina.com
Fri Sep 19 05:43:01 UTC 2003

On Thu, Sep 18, 2003 at 03:22:51PM -0500, Alexander Lazarevich wrote:
> Hi,
> We have lvm-1.0.3-4 running on RH Linux 7.3 (2.4.20-20.7smp). Hardware 
> is a Dell PE4600 with a PERC3 RAID controller. This is our department 
> fileserver. We want to move to RH Enterprise ES Basic, but I have some 
> questions first:
> 1) Which lvm is built into the Enterprise kernel? lvm1 or lvm2?

LVM1 will be in AS 3.

> 2) Does LVM config stay on disk? What I mean is this: we have just one LV 
> on our RH 7.3 system. It is 500GB and on a RAID 5 array. That LV has an 
> ext3 filesystem on it. If I blow away the 7.3 system, and install 
> Enterprise onto that same partition, will Enterprise LVM be able to 
> recognize the LV on the RAID 5 array? OR is that just not possible. I'm 
> thinking that's not possible - that the system keeps functional info 
> about the volume that is NOT on the disk. We have tape backup, but I'd 
> rather not do a restore of 400GB if I don't have to. 

If the installation doesn't overwrite the partition on the RAID5,
it will get recognized after the system update (presumably it will be AS 3).

> 3) We want to keep LVM because we will need to expand that filesystem over 
> another RAID 5 array in the future. Has anyone had any experience 
> expanding an LV over two *hardware* RAID 5 arrays? It should work because 
> the system has no idea the RAID even exists, but I'm just curious if 
> anyone else has done it and knows it works well.

You can use as many RAID5 subsystems as Physical Volumes as you want to
(standard limit of Physical Volumes is 256 per VG in LVM1; no such limit
in LVM2). Just pvcreate the new one(s) and vgextend the VG.

> 3) We've had great exp with LVM so far. We've had to lvextend twice, both 
> times it worked flawlessly. The only drag is we have to umount the volume. 
> Any chance that sistina will be able to extend lv's while the volume is 
> mounted? All other major unix's have that (AIX, HP, IRIX, etc). It's about 
> time Linux does that by default, and help out the 24-7-365 folks.

This is no LVM constraint. It is a constraint with the ext3 filesystem
which doesn't have an online resizer (yet).

If you want to resize online, you want to think about other filesystems
(e.g. reiser or xfs).

> Any advice is greatly appreciated, and thanks in advance.
> Alex
> ---                                                               ---
>    Alex Lazarevich | Systems Administrator | Imaging Technology Group
>             Beckman Institute - University of Illinois
>        alazarev at itg.uiuc.edu | (217)244-1565 | www.itg.uiuc.edu
> ---                                                               ---
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Heinz    -- The LVM Guy --

*** Software bugs are stupid.
    Nevertheless it needs not so stupid people to solve them ***


Heinz Mauelshagen                                 Sistina Software Inc.
Senior Consultant/Developer                       Am Sonnenhang 11
                                                  56242 Marienrachdorf
Mauelshagen at Sistina.com                           +49 2626 141200
                                                       FAX 924446

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