On Tue, Jun 23, 2015 at 03:30:43PM -0400, Matthew Wilcox wrote:

quoted

I can't make any guarantees, especially not without verification.  But
if correctly implemented any filesystems that does out of place metadata
writes (and that includes a traditional log) and uses checksum to ensure
the integrity of these updates it should be fine.  You'd still have
the issue of sector atomicy of file I/O though.

Is ext4 one of the filesystems that copes with torn updates to the log?
I see there's a checksum in the tail of at least some blocks, but I'd
like someone who understands ext4 to reassure me that it also doesn't
need the ability to put its log on a BTT.

In theory it should if the log checksums are enabled, but I wouldn't rely
on it without without confirmation and validation from the ext4 folks.