geom_raid5 inclusion in HEAD?
韓家標 Bill Hacker
askbill at conducive.net
Wed Nov 7 06:01:46 PST 2007
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
>>> Yes, AFAIK this would work.
>> A RAID5 is one of the harder ones to do both fast and well in
>> 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....
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