@martin @daftaupe
Tried btrfs à long time ago. Snapshots Can be great for OS Drive. But for data storage nothing Can Beat mdadm+lvm2. Big problem with btrfs : you can't know how much space is still available. (At the Time i checked it at least.)

@hoper @martin You can use btrfs filesystem df for example to know how much space is available (or used). or btrfs filesystem du to get details about a particular file.

@daftaupe @martin
Seems that things change, but according to the FAQ, there are still some issues with this matter (know how much Space left and use it)
btrfs.wiki.kernel.org/index.ph
Il still think that mixing réplication (raid) and file system is a very bad idea.

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@hoper @daftaupe @martin why would you think mixing FS/RAID is a bad idea? I'd argue it is a very good idea :)

@fink @daftaupe @martin
This break the "layer" model. i have 3 layer : raid, volume management, and fs (Can Swap the two first). If one of them is upgraded or replace by another, no problem. This also respect the unix philosophy : do a single thing, but do it well. Computing had always used layer model (network...). Because it's good and reliable. And for me, keeping my data safe is the most important thing.

@hoper @fink @martin Talking about data safety I wonder why Synology is recommending btrfs (they probably want to take the risk of putting their customers data in danger), synology.com/en-us/dsm/Btrfs. I think you might be interested about the paragraph related to data corruption. By the way which fs are you using that provides the same features ?

@daftaupe @fink @martin
Just checked this link, thanks.
Metadata miroring is a FS feature. For exemple ext4 make many copy of the superbloc. Guess that one day ext(5?) will offer more. In fact, I don't feel the need to have multiple copy of metadata because :

hardware problems (badblock) can't be an issue anymore with raidX

Logical problem (silent corruption) is also an issue already solved by mdadm with raid6. (callded "self healing" on synology link)

For last feature, snapshots >LVM.

@fink @daftaupe @martin
So yes, btrfs have more functionality. Some of them can be really great for OS drive (said it before). Allow rollback after an upgrade, snapshot per file and so on. But for the data... I don't need more functionality, I need something 100% stable, repairable on worst scénario, and wich make me feel secure. Because I can tell exactly how my files are stored, exactly where on the drives etc.

@fink @daftaupe @martin
Last thing about the layer model. Sometimes you don't need all layers. For example you don't always need a file system. Think about swap, or about oracle or other database software that will work better if you just give them raw devices, because they have their own integrated "file system". Can you make a "raw volume" (without any fs or metadata or whatever on it) with btrfs ?

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