Re: [PLUG] Mirrored drives with LVM

On Thu, May 22, 2008 at 1:27 AM, JP Vossen <jp@jpsdomain.org> wrote:

Got this one working, though I haven't fully explored installing grub on
the second drive, or "yanking" a drive to see how it does. Also, I'm
doing my testing in VMware at the moment, with small disks, as will be
obvious.

The goal for this one was to mirror both /boot and / (as James
suggested), but use LVM for /. It basically Just Worked, using the
Ubuntu Server (or probably Alternate CD, though I didn't test that).

I believe if you use the guided partioning with LVM, it uses the entire
disk for the volume group, then the entire volume group for the logical
volume (Debian Etch did anyway). THAT's BAD. You want to leave 2-4G of
space in the VG unused, so you can create LVM snapshots during backups.

Using Ubuntu Server CD; mirrored (/boot, /) + LVM
Partition Method: manual
Partition 256M as "physical volume for RAID" on both disks,
and flag bootable
Use the rest of each disk for "physical volume for RAID"
"Configure Software Raid"
Yes, to write changes
"Create MD devices"
RAID1 #0, then follow prompts, use 2, 0, then the
"boot" partitions
"Create MD devices"
RAID1 #1, then follow prompts, use 2, 0, then the
other partitions
RAID1 #0, set as "ext3", /boot, label "boot"
RAID1 #1, set as "physical volume for LVM"
Configure the LVM
Create volume group, name = vg_hostname
Create logical volume
lv_swap_1 512M
lv_root rest of space - e.g., 2G (to leave some
space free for snapshots!)
LVM VG vg_hostname, LV lv_root
Mount as ext3 /root, label = root
LVM VG vg_hostname, LV lv_swap_1
Use as swap area

The final partition setup should look something like this (tested from
in VMware):
LVM VG vg_hostname, LV lv_root - 7.1 GB Linux device-mapper
#1 7.1 GB f ext3 /
LVM VG vg_hostname, LV lv_swap_1 - 536.8 MB Linux device-mapper
#1 536.9 MB f swap swap
RAID1 device #0 - 254.9 MB Software RAID Device
#1 254.9 MB F ext3 /boot
RAID1 device #1 - 8.3 GB Software RAID Device
#1 8.3 GM K lvm
SCSI3 (0,0,0) (sda) - 8.6 GB VMware, VMware Virtual...
#1 primary 255.0 MB B K raid
#2 primary 8.3 GB K raid
SCSI3 (0,1,0) (sdb) - 8.6 GB VMware, VMware Virtual...
#1 primary 255.0 MB B K raid
#2 primary 8.3 GB K raid

I name the volume group vg_hostname, where hostname is actually the name
of the machine. I then name the logical volumes lv_whatever. lv_swap_1
is probably overkill, but it allows for adding more swap later. I
picked up that convention someplace on the 'Net, but if anyone has any
better ideas please share. I find the vg_ and lv_ parts useful since
the additional layers of abstraction created by LVM can get confusing,
especially if you only ever deal with it once every couple of years,
like I do.

Hope this is useful for someone,
JP
----------------------------|:::======|-------------------------------
JP Vossen, CISSP |:::======| jp{at}jpsdomain{dot}org
My Account, My Opinions |=========| http://www.jpsdomain.org/
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