[dm-devel] [PATCH] md/raid0: Fail BIOs if their underlying block device is gone

[Guilherme G. Piccoli]

On 29/07/2019 17:36, Roman Mamedov wrote:
> On Mon, 29 Jul 2019 17:27:15 -0300
> "Guilherme G. Piccoli" <gpiccoli at canonical.com> wrote:
> 
>> Hi Roman, I don't think this is usual setup. I understand that there are
>> RAID10 (also known as RAID 0+1) in which we can have like 4 devices, and
>> they pair in 2 sets of two disks using stripping, then these sets are
>> paired using mirroring. This is handled by raid10 driver however, so it
>> won't suffer for this issue.
>>
>> I don't think it's common or even makes sense to back a raid1 with 2
>> pure raid0 devices.
> 
> It might be not a usual setup, but it is a nice possibility that you get with
> MD. If for the moment you don't have drives of the needed size, but have
> smaller drives. E.g.:
> 
> - had a 2x1TB RAID1;
> - one disk fails;
> - no 1TB disks at hand;
> - but lots of 500GB disks;
> - let's make a 2x500GB RAID0 and have that stand in for the missing 1TB
> member for the time being;
> 
> Or here's for a detailed rationale of a more permanent scenario:
> https://louwrentius.com/building-a-raid-6-array-of-mixed-drives.html
> 

Oh, that's nice to know, thanks for the clarification Roman.
I wasn't aware this was more or less common.

Anyway, I agree with you: in this case, it's a weak point of raid0 to be
so slow to react in case of failures in one member. I hope this patch
helps to alleviate the issue.
Cheers,


Guilherme