Re: [PATCH 14/15] libnvdimm: support read-only btt backing devices

Christoph Hellwig
2015-06-24T12:11:53Z

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