Re: [PATCH] bcache: make stripe_size configurable and persistent for hardware raid5/6

[Eric Wheeler]

On Mon, 10 Jan 2022, Martin K. Petersen wrote:
> > Ok so `git blame` shows that Kent added this to md/raid5.c in 
> > c78afc6261b (Kent Overstreet 2013-07-11 22:39:53 -0700 7526)
> 
> Yep.
> 
> > Do you think we should leave the md-specific
> > raid_partial_stripes_expensive setting and require users of RAID
> > controllers to set the bit themselves in bcache---or---remove all
> > raid_partial_stripes_expensive code and always treat writes as
> > "expensive" when `opt_io` is defined?
> 
> I'd prefer the latter since that was the very intent of exporting the
> device topology in an abstract and protocol-independent fashion.
> However, I don't know enough about bcache internals to know whether it
> is always the right choice, what the trade-offs are, etc.

I've not looked in detail, but I don't think its too difficult.

Do you know if io_opt can be configured on scsi devices that do not have 
io_opt provided by the controller?  If so, or if it would be easy to add, 
then configuring io_opt at the scsi layer is probably a better option so 
subsystems besides bcache would benefit.

What do you think?

--
Eric Wheeler


> 
> -- 
> Martin K. Petersen	Oracle Linux Engineering
>