Re: [RFC] Draft Linux kernel interfaces for ZBC drives

[Jeff Moyer <jmoyer@redhat.com>]

"Theodore Ts'o" <tytso@mit.edu> writes:

> On Mon, Feb 03, 2014 at 04:01:15PM -0500, Jeff Moyer wrote:
>> "Theodore Ts'o" <tytso@mit.edu> writes:
>> 
>> >  * We can also further shrink the structure by removing the
>> >  * z_checkpoint_offset element, since most of the time
>> >  * z_write_ptr_offset and z_checkpoint_offset will be the same.  The
>> >  * only time they will be different is after a write is interrupted
>> >  * via an unexpected power removal
>> 
>> This may fall into the nit-picking category, but at runtime I'd expect
>> the write pointer and the checkpoint lba to be different more often than
>> not, unless you're doing all FUA writes, or are issuing flushes after
>> every write.
>
> Sure, but the only time we care is after an unexpected power removal,
> and I would expect that shortly after the system is rebooted, the file
> system or userspace storage space application would want to take care
> of dealing with recovery right away.
>
> So I'm not really proposing to track the z_checkpoint_offset except
> report writes to the storage device that might have failed due to
> power failures, since presumably this is the only time users of this
> interface would care.

I agree it would be silly to track the checkpoint lba.  I only took
issue with your comment.  ;-)

Cheers,
Jeff