[UBIFS] Filesystem capacity

[Jamie Lokier]

Artem Bityutskiy wrote:
> OK, then indeed Adrian wrote exactly the right thing. You have huge
> 4144-byte uncompressible nodes. You fit 3 of them to each eraseblock,
> and you waste 3440 bytes in each eraseblock. JFFS2 would jam a little
> more data, because it can split big blocks on parts.
> 
> In real life you will likely have compressible data, and many small
> files, so you will have small data nodes and many inode nodes, which
> are 160 bytes in size, so you will fit more.

Also, in real life, JFFS2 will behave badly when the filesystem is
completely full.  Its garbage collector can use 100% CPU for minutes
even on a small NOR flash, if the filesystem fills up too much.  It
happens because it's difficult to reorganise the data when there's no
spare room.

I wonder if the "lost" space in UBIFS is helpful to prevent long
garbage collection cycles?

-- Jamie