Date: Wed, 07 Nov 2007 09:01:27 -0500 From: =?UTF-8?B?6Z+T5a625qiZIEJpbGwgSGFja2Vy?= <askbill@conducive.net> To: freebsd-current@freebsd.org Subject: Re: geom_raid5 inclusion in HEAD? Message-ID: <4731C537.9030101@conducive.net> In-Reply-To: <fgse36$lbe$1@ger.gmane.org> References: <fgs516$mj8$1@ger.gmane.org> <487375.1457.qm@web30309.mail.mud.yahoo.com> <9bbcef730711070450x308129b4rb18577c317eee197@mail.gmail.com> <4731B8DA.8010201@conducive.net> <fgse36$lbe$1@ger.gmane.org>
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Ivan Voras wrote: > 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. > 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
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