Re: geom_raid5 inclusion in HEAD?

Ivan Voras wrote:
> 韓家標 Bill Hacker wrote:
>> Ivan Voras wrote:
>>> On 07/11/2007, Arne Wörner <arne_woerner_at_yahoo.com> wrote:
> 
>>>> Maybe gjournal could help, because graid5 honors the BIO_FLUSH, but
>>>> that is
>>>> untested...
>>> Yes, AFAIK this would work.
>>>
>> A RAID5 is one of the harder ones to do both fast and well in
>> software-only.
>>
>> The better hardware ($$$) controllers have fast hardware XOR engines as
>> well as CPU-as-state-machines and battery-backed cache, and THEY have to
>> work hard.
> 
> I agree. But regarding the immediate topic of gjournal on graid5:
> gjournal has hooks in the UFS code to do full sync before journal switch
> (commit), which it then propagates to the devices and issues BIO_FLUSH,
> so it can offer both speed and reliability in this particular case.
> 
>> Given decent hardware & any UPS that costs less than the hardware
>> controller, these are 'choices' - not really show-stoppers.
> 
> In theory this is correct, in practice still many people don't know the
> choices they are implicitly making.
> 

I'm all for having it / improving it.

GEOM in general and GMIRROR in particular have been *magic* for us as they are 
much more safely managed over ssh in the absence of an IPMI, IP KVM, or serial 
link than even a good hardware RAID controller.

But I'd not like to see yet-another iteration of 'a little knowledge..' folk 
follow geom_raid5 as flavor-of-the-month, then expect coders to yet-again defy 
gravity when the inevitable bites 'em in the anatomy, either.

First we walk. THEN we run....

Bill