[SOLVED] LVM help

MartenH · 02-19-2010, 07:11 PM

Hello,

I have two drives (sde 120Gb) and sdh(250Gb) which I want to use for the following setup:

sde + 120Gb of sdh as a striped LVM as an ext4 partition
remaining 130Gb of sdh as a separate ext4 partition

I am able to use the build in partition manager in Mandriva to set up the rest of my disks and I can set up an LVM as planned above, but I find no way of choosing whether it should be linear or striped. This means I will most likely have to do it from the command line. Can someone help me out with the correct commands to set it up? Please?

PS. I'm using Mandriva 2010.

ongte · 02-19-2010, 08:56 PM

Stripes can be defined at the creation of the LV.

For example:

Quote:

# lvcreate -i2 -I4 -L200G -n lv_striped vg00 /dev/sde /dev/sdh

Creates a striped LV named lv_striped that is striped across two PVs (/dev/sde and /dev/sdh) with stripe size 4KB and 200GB in size.

MartenH · 02-20-2010, 07:20 AM

Hello,

With the help of ongte and some more googling I was able to set it up as desired. Here is how I did it (as help for other users).

Create Physical Volumes (Partitions, not physical drives, the name is a bit confusing.)
Create partitions of all parts that should be included. This can be done using fdisk but I used the partition configurator in Mandriva. If you use Mandriva select Logical Disk Volume Manager as type (toggle to expert mode). If you use fdisk make sure to mark them as 0x8e (Some pages say 0xFE but that seems to be the old standard)

For me this meant making sde as one entire partition and then an equal size partition on sdh. (The remaining space on sdh was set up as a regular ext4 partition).
Register the Physical Volumes with LVM
This is done automatically in Mandriva partitioner. Otherwise you can use the following command:
>pvcreate /dev/sde1
>pvcreate /dev/sdh1
Create a volume group (vg0)
This can be done in the Mandriva partitioner by selecting each partition and choosing "add to LVM". Add both to a new Volume Group named vg0.
>vgcreate vg0 /dev/sde1
>vgextend vg0 /dev/sdh1

3b. Verify the volume group by issuing the command:
>vgdisplay -v vg0
Create a striped logical volume (lg0) in volume group vg0
I was not able to figure out how to do this in Mandrivas partitioner so I used the following command:
>lvcreate -l100%FREE -nlv0 -i2 vg0 /dev/sde1 /dev/sdh1

-l100%FREE tells it to use the entire amount of space on the partitions. You could also read the physical Extents (PE) from the vgdisplay command and type in the total sum. Or use a lower percentage/amount.
-nlv0 names the the Logical Volume
-i2 tells it to stripe it across the two disks.
vg0 is which volume group to use
/dev/sde1 /dev/sdh1 adds the two physical volumes (partitions) to use

Judging from ongtes comment you could also use -I to specify the stripe size. Default is 64KB which is what I have. I am not sure of the benefit of making it higher/lower. If ongte or anyone else care to comment on the choice of stripe size I'd be very happy!
Verify your logical volume:
>lvdisplay -v /dev/vg0/lv0
Mount it:
>mount /dev/vg0/lv0 /media/mountposition

Thanks to ongte and the following two pages
http://blog.fosketts.net/guides/walk...manager-linux/
http://linux.die.net/man/8/lvcreate

ongte · 02-20-2010, 08:55 AM

Glad you've got it working. As for stripe size, that largely depends on your environment & needs.
Obviously, if you have no idea, you can't go wrong choosing something in the middle. So 64KB makes sense as the default. There's really no reason to change that unless you have very specific performance requirements.

MartenH · 02-20-2010, 03:59 PM

Dang.

I thought I had it up and running. Tge lv0 was created, formatted, mounted. Added to fstab. Everything seemed fine.
...Reboot...
Now it won't work. lvdisplay for lv0 lists the lv0 but with "LV Status: NOT available".

Code:

[root@localhost]# lvdisplay
File descriptor 7 (/proc/1903/status) leaked on lvdisplay invocation. Parent PID 2873: bash
  /proc/misc: No entry for device-mapper found
  Is device-mapper driver missing from kernel?
  Failure to communicate with kernel device-mapper driver.
  --- Logical volume ---
  LV Name                /dev/vg0/lv0
  VG Name                vg0
  LV UUID                wpYl01-4J9y-Y3s8-Nt8n-oNRf-NRVs-o6BBjL
  LV Write Access        read/write
  LV Status              NOT available
  LV Size                228.98 GB
  Current LE             58618
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto

Why won't it stick? Is there some change I must do to make the lv persitent after a reboot?

Additional information:

Code:

[root@localhost]# lvchange -ay lv0
File descriptor 7 (/proc/1903/status) leaked on lvchange invocation. Parent PID 2873: bash
  Volume group "lv0" not found
  Skipping volume group lv0
[root@localhost]# lvchange -ay /dev/vg0/lv0
File descriptor 7 (/proc/1903/status) leaked on lvchange invocation. Parent PID 2873: bash
  /proc/misc: No entry for device-mapper found
  Is device-mapper driver missing from kernel?
  Failure to communicate with kernel device-mapper driver.

MartenH · 02-20-2010, 04:29 PM

It seems to be related to some modules not beeing loaded. Once I ran

Code:

modprobe dm_mod
modprobe dm_mirror
modprobe dm_snapshot

I could trigger lvchange -ay /dev/vg0/lv0 without a problem and remount it.

After a new reboot the modules have to manually started again. So, how can I set them up to run on startup?

MartenH · 02-20-2010, 04:53 PM

Problem solved. Add the following lines to /etc/modprobe.preload
dm_mod
dm_mirror
dm_snapshot