BTRFS RAID10 on Gentoo · uwot.eu
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BTRFS RAID10 on Gentoo

· by fabio · Read in about 2 min · (359 Words)
BTRFS Gentoo RAID

Btrfs is fairly stable and with the latest kernels it is becoming even a better alternative to the most commonly used EXT4 and XFS filesystems.
While not being always better or faster it brings to the table a huge amount of improvements that makes it by far the best filesystems for storage.
XFS itself is moving in the very same direction and will probably have in the near future some of the features Btrfs already has (e.g. copy on write).
No MDADM or partitioning is needed, to create a RAID10 with 4 HDD just type (where /dev/sd[X] is the disk whole disk, not a partition):

$ mkfs.btrfs -m raid10 -d raid10 /dev/sdb /dev/sdc /dev/sdd /dev/sde

To mount the volume at boot edit /etc/fstab accorgingly.

$ blkid /dev/sdb   # sdb can be any of the disks part of the RAID
xxxxxxxxxxxxxxxxxx

$ vi /etc/fstab
---
UUID=xxxxxxxxxxxxxxxxxx /mnt/data   btrfs   noatime,autodefrag 0 1

Mount options noatime and autodefrag are pretty much self explainatory: the first one tells the filesystem to not update the access time when a file is read while autodefrag tells it to keep files from being fragmented.
The utility btrfs can be used to manipulate and check Btrfs volume’s status.

### print general informations on every Btrfs filesystem
$ btrfs filesystem show
Label: 'raid10'  uuid: 30d7b40a-c14d-40e4-ac95-0adc54e8b347
    Total devices 4 FS bytes used 1.13TiB
    devid    1 size 1.82TiB used 581.51GiB path /dev/sdb
    devid    2 size 1.82TiB used 581.51GiB path /dev/sdc
    devid    3 size 1.82TiB used 581.51GiB path /dev/sdd
    devid    4 size 1.82TiB used 581.51GiB path /dev/sde

### change label of a mounted Btrfs filesystem
$ btrfs filesystem label raid10 /mnt/data/

In case the BTRFS volume is used to store some virtual machines it is highly advised to disable copy-on-write for the specific directory where they are stored.
To do so use the chattr command, also note that disabling copy-on-write for existing files cannot be done in place.
The correct procedure consists in creating a new folder, chattr +C that folder and then proceed to copy all the file from the old directory to the one with copy-on-write disabled.

$ chattr +C /path/to/directory

Linux Kernel wiki: https://btrfs.wiki.kernel.org/index.php/Main_Page
Gentoo Linux wiki: https://wiki.gentoo.org/wiki/Btrfs