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Old 16th April 2012, 09:12 AM
smannem Offline
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Join Date: Apr 2012
Location: Netherlands
Posts: 3
Question Partitioning Software RAID, LVM and BTRFS

I'm helping a friend setting up a website.
We use fysical server (with two equal harddisks of 500GB) from home.
I have some experience with Ubuntu and have recently switched to fedora.
I adviced using Fedora F16.
What I would like to do is:
- Create a RAID 1,
- Create LVM on this RAID
- Create some BTRFS partitions on this LVM

Why LVM and BTRFS? I want to isolate the partitions, so that filesystem running full has local effect (in one partition) only.
I had this working with Ubuntu 11.10 for a while. Latest friday I tried to create similar using Fedoira F16, but I ran into some issues:
- When I tried to create LVM PV on RAID device, An Error is displayed stating that RAID device can not be used with growable disks (or something).
- I worked around it using Ubuntu, but when I installed, only the first disk is bootable (e.a. when I remove te first disk no bootable partitions can be found.

Can you please advice:
- What is the best sollution for being able to boot degraded, and use flexible partitioning
- How should I configure this during installation

I'm looking forward to hearing from you...
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Old 30th April 2012, 12:20 PM
smannem Offline
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Join Date: Apr 2012
Location: Netherlands
Posts: 3
Re: Partitioning Software RAID, LVM and BTRFS

Jeez, guys.
Didn't expect it to be so difficult...
I'll try some things with a KVM VM and let everybody know when I have an answer...
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Old 3rd May 2012, 09:16 PM
smannem Offline
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Join Date: Apr 2012
Location: Netherlands
Posts: 3
Cool Re: Partitioning Software RAID, LVM and BTRFS

Seems to be a one man show. Well, I hope that this might help others.
I finally installed Fedora with good working SoftRAID.
How? Two caveats:
- There seems to be a bug in the installer with the MD Creation proces.
When you want to create the array a message is printed:
Only RAID0 arrays can contain growable members.
I can't seem to fix it, so I create the partition layout at forehand.
- There is a bug in the process for detecting MD metadata version.
Read this for more info: https://bugzilla.redhat.com/show_bug.cgi?id=750480

This is what I do:
- I boot using the Fedora 16 DVD (64 bit)
- I enter Rescue system
- I move forward untill I get a shell.
- I partition both disks the same
- Partition of 500MB
- Partition of the rest of the diskspace
- I create a SoftRAID on the first partitions (mdadm -C /dev/md0 -n 2 -e 0.9 /dev/vda1 /dev/vdb1)
- I create a SoftRAID on the second partitions (mdadm -C /dev/md1 -n 2 -e 0.9 /dev/vda2 /dev/vdb2)
- I wait until both arrays are build
- I create an LVM Fysical device on md1, build Volume Group and Logical VOlumes
- I partition /dev/md0 using ext4 and all the others as I wish
- I reboot again using the Fedora 16 DVD (64 bit)
- On the Install section I press tab and enter ' updates=http://dlehman.fedorapeople.org/pdates/updates-750480.3.img' at the end of the line.
- In the disk layout page I choose all the partitions and configure their mount points (/dev/md0 = /boot).
- In the next page I choose that the boot sector is written to the disk (/dev/vda in my testcase), and not to my SoftRaid device (/dev/md0)
- I finish the installation et voila.

When I disconnect one of my disks everything boots from the other, so I'm pleased...
Hope this might help anyone else too.
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Old 4th May 2012, 07:55 AM
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Re: Partitioning Software RAID, LVM and BTRFS

You need to STOP and think real hard about what you are doing and why.

Read up on btrfs for a while first.
BTRFS you can add multiple block devices to a singe filesystem (similar to adding PVs to an LVM)
BTRFS has a concept of subvolumes (similar to LVM logical volumes)
BTRFS has a concept of striped and mirrored storage - similar (not identical) to RAID-1 (and 0).
So putting a btrfs on top of LVM on top of RAID1 is certainly possible - but a waste of resources.
I wouldn't imagine anyone using btrfs on top of LVM.
I think only a minority would want to put btrfs on top of RAID0 or RAID1.

So maybe I don't understand your goals in detail - but this sounds like a silly approach.
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