On Fri, Aug 26, 2016 at 12:10 PM, Kent Overstreet 
[off-list ref] wrote:

On Thu, Aug 25, 2016 at 02:03:33PM +0200, Marcin Mirosław wrote:

quoted

 https://lwn.net/Articles/655183/ :
 "Caveat: don't try to use tiering and checksumming or compression 
at the
 same time yet, the read path needs to be reworked to handle both at 
the
 same time."

 Is it sill valid?

No, I did do that read path reworking, they should work.

However, I haven't been focusing on or exercising the multi device 
stuff in
quite awhile - my main priority has been making single device 
filesystems rock
solid and finishing off compression and such.

Tiering ought to work, but can you hold off on exercising anything 
else? e.g.
the active/RO transition stuff - I'm going to have to spend a fair 
amount of
time digging into that code and figuring out what makes sense when 
the time
comes.

The checksum error is highly concerning though - that was related to 
messing
with cache0/state, correct? I think Christopher is using tiering with
checksumming enabled, can you confirm?

Yup. I've got two tiered filesystems; one nvme in front of two HDDs 
with crc32 checksums, and one regular SSD in front of a HDD with crc32 
and lz4 compression.

Neither have had significant problems.