For me bcachefs provides a feature no other filesystem on Linux has: automated tiered storage. I've wanted this ever since I got an SSD more than 10 years ago, but filesystems move slow.

A block level cache like bcache (not fs) and dm-cache handles it less ideally, and doesn't leave the SSD space as usable space. As a home user, 2TB of SSDs is 2TB of space I'd rather have. ZFS's ZIL is similar, not leaving it as usable space. Btrfs has some recent work in differentiating drives to store metadata on the faster drives (allocator hints), but that only does metadata as there is no handling of moving data to HDDs over time. Even Microsoft's ReFS does tiered storage I believe.

I just want to have 1 or 2 SSDs, with 1 or 2 HDDs in a single filesystem that gets the advantages of SSDs with recently used files and new writes, and moves all the LRU files to the HDDs. And probably keep all the metadata on the SSDs too.

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guenthert 3 days ago | parent [-]

> automated tiered storage. I've wanted this ever since I got an SSD more than 10 years ago, but filesystems move slow.

You were not alone. However, things changed, namely SSD continued to become cheaper and grew in capacity. I'd think most active data is these days on SSDs (certainly in most desktops, most servers which aren't explicit file or DB servers and all mobile and embedded devices), the role of spinning rust being more and more archiving (if found in a system at all).

	▲	wtallis 3 days ago \| parent \| next [-]
		Tiering didn't go away with the migration to all-SSD storage. It just got somewhat hidden. All consumer SSDs are doing tiered storage within the drive, using drive-specific heuristics that are completely undocumented, and host software rarely if ever makes use of features that exist to provide hints to the SSD to allow its tiering/caching to be more intelligent. In the server space, most SSDs aren't doing this kind of caching, but it's definitely not unheard-of.
	▲	ThatPlayer 2 days ago \| parent \| prev \| next [-]
		Yeah, for enterprise where you can have dedicated machines for single use (and $) there probably isn't much appeal. That's why I emphasized as a home user, where all my machines are running various applications. Also for video games, where performance matters, game sizes are huge, and it's nice to have a bunch of games installed.
	▲	jcgl 2 days ago \| parent \| prev [-]
		Until $/GB drops to comparable to HDDs, large-scale storage will continue to use HDDs.