Btrfs and Raid setup

[eusanpe]

Hello All,

I have been using reiser4 for a couple of years now but I am tired of the fsync issues that hamper my system so I am going to
change. I just purchased two 500gb 7200 rpm hard drives for my laptop. I am going to try btrfs along with a raid0 setup. I have
some questions though.

1. For the partitions, should I use gdisk to create all primary partitions or fdisk along with LVM? This is going to be an all/only
Gentoo system. I will have partitions for /home /usr/portage/distfiles /usr along with some others
2. I am going to use Raid0 (striping) on my partitions, should /boot be set to Raid1 (mirroring)? What about swap?
3. How does btrfs raid setup compare to mdadm setup. I just want some experiences from some of the ones who have tried both.
4. Are there any special flags to use along side mkfs.btrfs besides raid setup to get maximum performance, ex..sectorsize, etc...
5. How is compress-force running in a raid0 setup?


Thank you for any advice.
Tony

[ToeiRei]

[fangorn]

As a follow up:

GRUB also can't boot from RAID. But RAID1 for /boot is as if you didn't use RAID at all, so this will work.

There already is some kind of load balancing between multiple swap partitions, so RAID is not advisable.

concerning RAID in btrfs:
btrfs is still in heavy development and AFAIK not even the ondisk format is fix.

btrfs is fit for testing purposes IMHO, but if it hurts you to rebuild everything from scratch, then don't use the more advanced features. And if you do, keep good backups of each and every file on the disks.

That said, I'd recommend md RAID (and LVM if needed) solution at this point of time.
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[ToeiRei]

I am running btrfs as my rootfs for quite a while now. As long as you don't do many funky things it should be quite stable and the experimental flag is about to be removed in the next kernel versions
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[fangorn]

Yeah, but I for my part see the subvolume and RAID part as "funky features".

I use them only at test disks where I don't put any data I don't have elsewhere. The system device is IMHO not suitable for testing them.

I am with you that btrfs is fit for being "just a filesystem" for a single partition, but that is not where it's strengths are. In these sectors there are plenty of filesystems that can compete. There I for my part tend to use well tested filesystems (ext3 for / and home, xfs for data storage).
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[EzInKy]

[eusanpe]

Thank ya for the advice. After eight years of using Gentoo/Funtoo and '~amd64', I backup my system nightly because you never know
what could happen.

So do I create the /boot and swap partitions on /dev/sda (/dev/sda1 and /dev/sda2) and then rootfs(/) on sda3 and then rootfs(/) on sdb1 and
join both rootfs partitions via raid0 and create subvolumes for /home and other directories that would previously be partitions?

I currently use LVM but btrfs seems so much easier since it is all integrated.


Thanks again,
Tony

[eusanpe]

Is there a btrfs howto or can anyone let me know how to setup subvolumes for the root filesystem in Gentoo? For instance how to create a /var/tmp or /usr/portage/distfiles subvolume
during install. I am doing a brand new install using System Rescue CD. I have partitions setup as:

/dev/sda1 /boot ext2
/dev/sda2 /rescuecd ext2
/dev/sda3 swap
/dev/sda4 / btrfs

I have been looking at some links about this but they aren't Gentoo specific. Any advice would be appreciated.


Thanks.

[fangorn]

No gentoo specific documentation should be needed.

emerge btrfs-progs

and use the documentation for creating and mounting subvolumes from anywhere you trust.

While installing you might want to choose a live-cd that already has btrfs-progs installed.
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[Veldrin]

I only have experience with btrfs on a single drive, but I will provide my insights....

As good starting point is the btrfs wiki which tells you about how to configure it.

Live Systems
As live environment (also for any rescue and backup operations, i can anything goes wrong) I prefer SystemRescueCD

Creating a btrfs Volume
The basic steps are the following:

• create a btrfs volume (e.g mkfs.btrfs /dev/sda3 )
  
• mount the volume (e.g mount -t btrfs /dev/sda3 /mnt/btrfs )
  
• create subvolumes (e.g system and var: btrfsctl -S system /mnt/btrfs && btrfsctl -S var /mnt/btrfs )
  Subvolumes are (simply put) just directories within the volume. And you should never mount the "root"volume unless you want to manipulate the subvolumes/snapshots.
  
• umount the volume (umount /mnt/btrfs )
  not necessary, but helps to avoid confusion
  
• mount the subvolumes (e.g mount -t btrfs /dev/sda3 -o subvol=system/mnt/gentoo && mkdir /mnt/gentoo/var && mount -t btrfs -o subvol=var /dev/sda3 /mnt/gentoo/var )
  
• fix the root permissions ( e.g chmod 755 /mnt/gentoo )
  otherwise only root is able to access the partition, as by default the permission is set to 700

Changes for multidevice setup
There is only one small difference in creating a multidevice setup: (linky)
only the volume creation step need some change. (e.g mkfs.btrfs /dev/sda3 /dev/sdb3 )

As mentioned above, I have not tried this, an I am not sure about its implications. From Reading the documentation, you can specify what kind of raid will be created (0, 1, 10 are currently supported), and how the metadata and journal are used.

There is no changes in how those partitions are mounted.

fstab and grub.conf
moving on with the above example, the would be the fstab entries and grub.conf (irrelevant parts are omitted.)

(var uses the built-in compression)

[Veldrin]

I kind of missed your core questions....

how to create and use subvolumes for /usr/portage/distfiles and /var/tmp
Assuming that your btrfs volume resides on /dev/sda3, and all of the above steps have been done (i.e creating subvols system and var)

[eusanpe]

[Veldrin]

Sry - I did too much of copy/paste.

Of course you are right, and the subvol needs to be mouned in the correct place.

*shame on me*
V.

[eusanpe]

No problem. This is a great starter. I am running btrfs on one 500 gb drive with one btrfs partition. It runs great so far compared to Reiser4. I have had
no fsync issues. I am going to try this on a new install and see.

Thank you again.

Tony

[eusanpe]

I set things up and everything installed perfectly except the boot process. I have a Raid0 array setup. When I boot I am getting a kernel panic. If I boot to my rescue disk and run manually
'btrfsctl -a', I can then mount. I have been reading the wiki regarding initramfs but I can't get the busybox init script named 'init'. I am not running genkernel. Can anyone tell me what my busybox
script should look like to boot this raid?

My raid0 partitions are /dev/sda4 and /dev/sdb1. I have the libraries for btrfsctl in a directory called /initramfs/lib, btrfsctl in /initramfs/sbin and busybox compiled with the USE flag 'static''
and the binary copied to /initramfs/bin. I added just 'btrfsctl -a' in the busybox script named 'init' and it runs it but then it panics again. The error is:

Kernel Panic - not syncing: attempted to kill init.


Thanks again,
Tony

[fangorn]

[eusanpe]

Thank you for the reply.

I have the same thing in my grub config file. Everywhere I was reading specified that I needed an initrd to setup a raid0 root drive. I will keep on messing with it.
Do you have a raid setup on your laptop using btrfs?


Thanks,
Tony

[fangorn]

OK, I did not realize you had RAID0.

In this case: yes, you need an initrd.

But not because of btrfs.
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[aoeuaoue]

just to share my experience

raid0 with three 1tB drives, pretty solid. Make sure that all your drives mach the same throughput or else your hardrives will be limited to the lowest one. I learned this the hard way.

for testing I mounted /usr/portage with compress option, now portage tree is only 167M. Now I wander where else should I try this.

[eusanpe]