Btrfs is a filesystem (like FAT, NTFS, and ext4), but has some distinct advantages:
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Increased storage - thanks to compression and file deduplication, Btrfs can save you considerable amounts of storage. I have 517G of files on my Deck’s SSD, but it only uses up 410G of storage to hold those files. Compressing your filesystem can also shorten load times, especially for slower memory devices like the SD card.
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Snapshotting - save snapshots of the file system and easily roll back if there’s a problem.
Converting to Btrfs is easy to do, and doesn’t require having you to resetup/reconfigure your deck. The linked gitlab project will do the conversion, keep all your existing files and settings, and set all the Btrfs configurations for you. The file conversion will persist through updates, and it will setup automatic deduplication of files on the drive. It also allows the Deck to automatically mount Btrfs converted SD cards, and to format new cards in the same format.
Only potential downside I know of is that Btrfs is case sensitive, where the default ext4 on the Deck uses casefolding. Basically this means that Btrfs will treat File.txt and file.txt as two different files. I’ve never run into any issues with this, but I’ve heard it can cause issues with some specific mods that inconsistently capitalize their files. There’s also always some risk whenever you make dramatic changes to your filesystem, but I haven’t really heard of anyone having problems with this. You do have to make sure you have at least 10-20% of your storage free (and a min of 10-20GB free for smaller drives) to make sure it has room for the conversion.
Overall I’ve been using Btrfs for over 6+ months on my deck, and it’s been great. I highly recommend it. I’m not an expert on it, but I’ll do my best to answer any questions on it.
If you can do that, you already had enough space for reflinking not to matter in the first place, right? Or you can carefully do defragmenting in parts, running dupremove incrementally? seems like a lot of wasted time :).
Free storage is free storage, and storage is at a premium on the Steam Deck - I would gladly trade time for storage, considering that time passes regardless. This defrag scenario would only happen if you want to change ZSTD levels, so if you pick your level at the start, copy your data on, then run
duperemoveyou’ll save the most space possible without needing to defrag. Deduplication is probably the difference between being able to fit 1-2 more games on your Steam Deck - Wine prefixes are prime targets for deduplication.