Re: [bcachefs][tier] kernel BUG at drivers/md/bcache/super.c:1561! after double changing state of device

[Christopher James Halse Rogers <chris@cooperteam.net>]

On Fri, Aug 26, 2016 at 12:10 PM, Kent Overstreet 
<kent.overstreet@gmail.com> wrote:
> On Thu, Aug 25, 2016 at 02:03:33PM +0200, Marcin Mirosław wrote:
>>  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.