Is btrfs ready to be default fs in F17 ?

[Alan Cox]

> I´ve run Btree based HPFS for over a decade...
> http://pages.cs.wisc.edu/~bolo/shipyard/hpfs.html

HPFS is for the most part a traditional Unix file system with cylinder
groups.

You have superblock (block 16), and then 8MB bands of data with
allocation bitmaps between them. Sound familiar ? It also does
pre-allocation and give back (as ext3/4 now do with reservations) but has
no journalling.

So its really a BSD FFS like file system with fancier metadata. That's
completely different to a b-tree/b+tree file system like reiserfs3 or
btrfs. In particular it uses btrees within objects only. So corrupting
the btree of an FNODE loses you a file and your coherency checking
problem for the tree is internal to each object. A DIRBLK is perhaps
slightly worse news but you've still got the FNODE so you can find the
contents of everything.

Apple HFS/HFS+ has a similar sort of design. Ask any long term MacOS
user about the dreaded "Invalid B-tree node" message which is usually
followed by "Error: File system verify or repair failed"

Alan