8000 QUESTION : Why use a btrfs blank snapshot instead of tmpfs ? · Issue #11 · Misterio77/nix-config · GitHub
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QUESTION : Why use a btrfs blank snapshot instead of tmpfs ? #11

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Nandicre2 opened this issue Feb 25, 2023 · 10 comments
Open

QUESTION : Why use a btrfs blank snapshot instead of tmpfs ? #11

Nandicre2 opened this issue Feb 25, 2023 · 10 comments

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@Nandicre2
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Just asking, because i tought that snapshoting was bad for the SSD longetivity.
@Misterio77
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Hello!

I'm actually considering moving back to ext4+tmpfs, because of simplicity mostly.

Btrfs does have a couple of goodies that might make it worth using:

  • Snapshots: useful to have lightweight "backups" (for human error situation, that is) for your data
  • Transparent compression: shaves off about 20-30% storage with negligible performance impact
  • Subvolumes: you can have logical volumes within the same physical partition, making it pretty painless to organize stuff into different mountpoints if needed

@Nandicre2 Nandicre2 reopened this Feb 26, 2023
@Nandicre2
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(sorry for the open and close, was answering from my phone)

I'm actually considering using both : tmpfs as root and everything else on btrfs. I found this blog post and I think I'll go this way

@luxus
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luxus commented Feb 26, 2023

would https://github.com/nix-community/disko not help with the "its complicated" part? didn't checked it out yet.

@Nandicre2
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would https://github.com/nix-community/disko not help with the "its complicated" part? didn't checked it out yet.

Didn't checked it out either. I've seen it mentioned on the forum but i don't want to mess with it now. Maybe later

@Misterio77
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would https://github.com/nix-community/disko not help with the "its complicated" part? didn't checked it out yet.

Disko is pretty cool. Moving my setup to it is definitively on my todo-list.

@ghost
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ghost commented May 3, 2023 •
edited by ghost
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My issue with tmpfs is that you have to specify a size for the tmpfs root or be limited based on your RAM. Tmpfs defaults to half your system RAM (I believe). Some guides set tmpfs to 2GiB (example), but that means that you can only have up to 2GiB of files on root outside of the files you have persisted on a separate partition. Btrfs' logical volumes avoid this by having automatically resizing subvolumes so I never have to think about the size of individual subvolumes.

@NerdHusky
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(sorry for the open and close, was answering from my phone)

I'm actually considering using both : tmpfs as root and everything else on btrfs. I found this blog post and I think I'll go this way

Nice post! Wish I'd found it sooner!
No really, I went with btrfs because it's really cool, I could make a raid with it without LVM it has compression (really 0 performance decrease with raid0) and...COW! ;)
Plus yeah some snapshotting for backup purposes do no harm I guess! ;) not to /nix of course, but /home and maybe /persist (especially when I'll wipe out even home at boot - the original post doesn't but I'll go for it once my home-manager configuration is really solid).

@NerdHusky
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My issue with tmpfs is that you have to specify a size for the tmpfs root or be limited based on your RAM. Tmpfs defaults to half your system RAM (I believe). Some guides set tmpfs to 2GiB (example), but that means that you can only have up to 2GiB of files on root outside of the files you have persisted on a separate partition. Btrfs' logical volumes avoid this by having automatically resizing subvolumes so I never have to think about the size of individual subvolumes.

That I didn't know and if it's true it really sucks because I'm already using zram xD.

@threddast
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I have been using tmpfs for a while, and to be honest it has its quirks, see for example nix-community/impermanence#124 . This issue is not present when root is on btrfs.

@musjj
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musjj commented Apr 25, 2025

How's the situation with tmpfs recently? Looking into impermanence, but ZFS/Btrfs is too much for me.

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@luxus @Misterio77 @threddast @musjj @Nandicre2 @NerdHusky
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