Timothy Shimmin wrote: > Also from memory, I believe Neil checked this removal into the SLES10sp1 tree > and some sgi boxes started having slow downs > (looking at Dave's email below - we were not wanting to tell them > to use nobarrier but needed it to work by default - I forget now). But that's an admin issue. The way it is now, for example a home user of md raid1 (me!) can't run barriers even if they wanted to. Until there is a way to know if a write cache is non-volatile the only safe option is to enable barriers when possible. > 6. >> Date: Wed, 25 Jun 2008 08:57:24 +1000 >> From: Dave Chinner <david@xxxxxxxxxxxxx> >> To: Eric Sandeen <sandeen@xxxxxxxxxxx> >> Cc: LinuxRaid <linux-raid@xxxxxxxxxxxxxxx>, xfs-oss <xfs@xxxxxxxxxxx> >> Subject: Re: md raid1 passes barriers, but xfs doesn't use them? >> >> Yeah, the problem was that last time this check was removed was >> that a bunch of existing hardware had barriers enabled on them when >> not necessary (e.g. had NVRAM) and they went 5x slower on MD raid1 >> devices. Having to change the root drive config on a wide install >> base was considered much more of support pain than leaving the >> check there. I guess that was more of a distro upgrade issue than >> a mainline problem, but that's the history. Hence I think we >> should probably do whatever everyone else is doing here.... >> >> Cheers, >> >> Dave. > > So I guess my question is whether there are cases where we are > going to be in trouble again. > Jeremy, do you see some problems? FWIW, the problem *I* foresee is that some people are going to slow down when using the defaults, yes, because barriers will start working again. But I don't see any other safe way around it. Education would be in order, I suppose. :) -Eric > --Tim > > > -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
