[dm-devel] [PATCH 2/2] md/raid0: Do not bypass blocking queue entered for raid0 bios

[Wols Lists]

On 08/05/19 15:52, Guilherme G. Piccoli wrote:
> Hi, I understand your concern. But all other raid levels contains
> failure-event mechanisms. For example, in all my tests with raid5 or
> raid1, it first complained the device was removed, then it failed in
> super_written() when no other available device was present.
> On the other hand, raid0 does "blind-writes": it just selects the device
> in which that bio should be written (given the stripe math) and change
> the bio's device, sending it back via generic_make_request(). It's
> dummy, but not in a bad way, but rather for performance reasons. It has
> no "intelligence" for failures, as all other raid levels.
> 
> That said, we could fix md.c for all raid levels, but I personally think
> it's a bazooka shot, only raid0 shows consistently this issue.
> 
The academic in me says we should push that error handling into
generic_make_request() or some raid function in md.c that deals with
those problems. Sounds like there's a fair bit of duplicate
functionality that could be re-factored out.
>>
>> Academic purity versus engineering practicality :-)
> 
> Heheh you have good points here! Thanks for the input =)
> Cheers,
> 
Doesn't help when there's not an architect to design an overall "grand
scheme", but my usual way of working is to design top down academically,
and then ask myself "what do I need" before implementing bottom-up.
Hopefully with a load of documentation saying "I haven't done this
because I don't need it, but this is where it goes".

Cheers,
Wol