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From: Ivan Voras <ivoras@freebsd.org>
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Subject: Re: geom_raid5 inclusion in HEAD?
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韓家標 Bill Hacker wrote:
> Ivan Voras wrote:
>> On 07/11/2007, Arne Wörner <arne_woerner@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.