[TriLUG] Problem with LVM

[Jon Carnes]

Sounds like this would make a great class.

A howto on setting up disks (and maybe other devices that act like
disks). And Brian seems like he would make a great instructor. :-)


On Sat, 2006-06-03 at 22:36, Brian McCullough wrote:
> On Sat, Jun 03, 2006 at 09:47:10PM -0400, T. Bryan wrote:
> > On Saturday 03 June 2006 09:14 pm, Brian McCullough wrote:
> > 
> > > Here, Rick is combining two different technologies, that may confuse
> > > you.  
> > 
> > Yes and no.  I am also trying to use LVM on top of a RAID 1 device.  Of 
> > course, since this is the first time I've created a software RAID under 
> > Linux, and it's also the first time I've used LVM....yeah, a bit of 
> > confusion.  :)
> > 
> > > The first, which is RAID ( type 1 -- Mirroring ) is what he used 
> > > sdb5 for.  Then he used LVM on top of that RAID device to create, first,
> > > a Physical Volume, and then a Volume Group ( VG ).  Yes it was
> > > unformatted, or if it wasn't he is in trouble!
> > 
> > I think that he's fine.  I don't think that I was.  My notes say that the 
> > first time I tried this, I did the following. 
> > 
> > Created /dev/hde1 and /dev/hdg1 as Linux partitions
> > Formatted both partitions as ext3
> > Created the RAID device /dev/md0 using /dev/hde1 and /dev/hdg1 
> > Created a physical volume on /dev/md0
> > Created a volume group on /dev/md0
> > 
> > Then the rest of the stuff that matched what Rick had done last time: 
> > creating volume groups, formatting the logical devices, mounting the 
> > logical devices.
> > So....when I try this again, I'll set the partition type to LVM, and 
> > I'll skip the part where I formatted the partition.  Perhaps that's 
> > how I got myself into trouble.  :)
> 
> Tom,
> 
> In a sense, you did things a bit upside down.  You have to think of both
> RAID and LVM as producing block devices, while your ultimate goal is a
> filesystem, formatted in the format you like. ( ext2, ext3, etc. )
> 
> As you understand, you need to layer things to get the effect that you
> want.  This is something that I tend to do for any client machine where
> things are worth saving -- RAID saves you from some hardware errors --
> it won't save you from typing "rm" but....  The RAID device is like one
> or more actual disk drives.  Then LVM allows you to assemble one or more
> "physical" disk devices into a seamless whole, which you then subdivide
> as necessary for your own partitioning scheme.  You also understand that
> this partitioning scheme is completely flexible, and that you can change
> the size of any "partition" as you like, when you like.  Up to this
> point, you are, in effect, dealing with the devices -- now you actually
> allocate, format and mount the various parts of your filesystem.
> 
> 
> Your procedure should be -- actually, you have two alternatives,
> although I will only give you the preferred one.
> 
> Use fdisk to create partitions for your RAID device or devices.  Each of
> those partitions will be coded as "fa" if I remember correctly -- it is
> the "automatic RAID partition type" -- check fdisk.  Then use mdadm to
> assemble each RAID device from the various partitions that comprise it.
> Once you have those RAID devices, use pvcreate to mark them as being
> initialized for LVM use.  This makes a mark in the first block of the
> RAID device ( or partition ) which LVM uses to identify devices that it
> is using.  Then use vgcreate to assemble the PVs into volume groups.
> This also makes marks in the partitions, showing them as belonging to
> that VG.  A record is also kept in /etc/lvm of all of this work, which
> should be backed up periodically. ( read up on vgcfgbackup /
> vgcfgrestore )  Finally, use lvcreate / mke2fs to create the actual 
> components of your filesystem.  Note, however, that in your lvm.conf
> file, you need to check your filters, to make sure that ONLY the "mdX"
> device is scanned, NOT the sdaX, sdbX devices.
> 
> 
> > ---Tom
> 
> 
> Brian
> 
> 
> ______________________________________________________________________
> 
> -- 
> TriLUG mailing list        : http://www.trilug.org/mailman/listinfo/trilug
> TriLUG Organizational FAQ  : http://trilug.org/faq/
> TriLUG Member Services FAQ : http://members.trilug.org/services_faq/