BTRFS subvolumes and the space they occupy explained

[SpecialEd]

Hey Ed,

GG's got it right with only two other considerations: EFI and GPT.

If you are planning on using a GPT partition table, you need the reserve a small partition for grub. Here's the How-To for that. This is no biggie as it uses space otherwise wasted on the disk if you do it my way.

The other is EFI, if you're using it you will need a small EFI partition (about 500MB). Worth considering is if you're using EFI you can use other boot managers rather than grub. Here's some info on all that.

So assuming Legacy boot (non-EFI) and using GPT partition table (I recommend it), and swap to hibernate too, you would need 3 partitions, 4 if you're using EFI.

As far as "mixing" HD and SSD on the same btrfs file system, I wouldn't recommend it for a couple reasons;
1) Because btrfs detects SSDs and adjust to them. I don't know what it would do if you mixed one with a HD, but I wouldn't do it without some research and testing.
2) You'd likely slow down the access to the SSD so much because you be sharing access time with the HD that you'd lose much of the benfefit of the SSD.

A better and safer course would be to have two btrfs file systems - one on each device - and use them separately, which you easily do by mounting subvolumes as needed. Plus then you can backup subvolumes from one device to the other and have a solid backup if one device fails.

Are there any downsides to formatting the drive connected via USB, before I actually install it into the laptop?

[oshunluvr]

Not that I'm aware of

[SpecialEd]

Not that I'm aware of

Cool, thanks.

[GreyGeek]

Are there any downsides to formatting the drive connected via USB, before I actually install it into the laptop?

Worked for me.
I all my offline USB HD's are formatted with btrfs as the fs