I am planning on creating a home server with either 2 (RAID1) or 3 (RAID5) HDDs as bulk storage and 1 SSD as bcache.
The question is, what file system should I use for the HDDs? I am thinking of ext4 or xfs, as I heard btrfs is not recommended for my use case for some reason.
Do you all have some advice to give on what file system to use, as well as some other tips?
I would just skip RAID, add all disk to a single BTRFS and use the built in profiles for (meta)data redundancy.
Cache I don’t know much tho.
The man page at https://btrfs.readthedocs.io/en/latest/mkfs.btrfs.html says:
RAID5/6 has known problems and should not be used in production.
So those profiles have unknown, unspecified problems.
But btrfs is safe on top of md-based raid1/5/6. It also has the advantage that you only need to encrypt one volume.
Could you elaborate on btrfs on top of md raid?
This one seems the most likely solution for me.
Sure. First you set up a RAID5/6 array in mdadm. This is a purely software thing, which is built into the Linux kernel. It doesn’t require any hardware RAID system. If you have 3-4 drives, RAID5 is probably best, and if you have 5+ drives RAID6 is probably best.
If your 3 blank drives are sdb1, sdc1, and sdd1, run this:
mdadm --create --verbose /dev/md0 --level=5 -n 3 /dev/sdb1 /dev/sdc1 /dev/sdd1
This will create a block device called /dev/md0 that you can use as if it were a single large hard drive.
mkfs.btrfs /dev/md0
That will make the filesystem on the block device.
mkdir /mnt/bigraid
mount /dev/md0 /mnt/bigraid
This creates a mount point and mounts the filesystem.
To get it to mount every time you boot, add an entry for this filesystem in /etc/fstab
Are there some advantages of btrfs over raid? I understand how raid works but btrfs for redundancy is foreign to me.
BTRFS has RAID built into the file system - instead of using MD you use BTRFS profiles which tell the system how to handle data.
For instance
- file system data (critical for the file system to function): raid1c3 which means 3 copies of core P file system data on 3 different devices
- user data: raid1 (so duplicating all your data on two different devices)
With this set up you could lose one device (of n, the total doesn’t matter), and not lose any data, and still be able to boot to recover with too much hassle.
BTRFS does block checksums, can scan for bit rot and recover from it, and generally tries to make your data safe. It technically supports raid5/6 for user data, the issue is around unclean shutdowns and a potential write hole where you could lose data, but if your system has a UPS backup and is on a relatively recent kernel it’s not any more dangerous than MD raid5/6 as I understand it.
I use BTRFS for snapshots, and auto compression. Maybe it can be done with raids with LVM? AFAIK BTRFS redundancy is basically the same as traditional RAID, similar to using mdadm. Still, you would want a backup strat instead relying on the disk redundancy. I learn that the hardway.
