Date: Thu, 30 Oct 2008 22:05:43 -0500 From: Rich Winkel <rich@math.missouri.edu> To: Jeremy Chadwick <koitsu@freebsd.org> Cc: Rich Winkel <rich@math.missouri.edu>, freebsd-questions@freebsd.org Subject: Re: Filesystem, RAID Question Message-ID: <20081031030543.GA58401@pencil.math.missouri.edu> In-Reply-To: <20081031023347.GA19474@icarus.home.lan> References: <9f3798c00810291118i1c80cb8cw8d4995eabe6a4f8f@mail.gmail.com> <4908BE2C.7010505@infracaninophile.co.uk> <20081030231207.GA56260@pencil.math.missouri.edu> <20081030233849.GA16747@icarus.home.lan> <20081031014159.GI22915@pencil.math.missouri.edu> <20081031023347.GA19474@icarus.home.lan>
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On Thu, Oct 30, 2008 at 07:33:47PM -0700, Jeremy Chadwick wrote: > > One of the main functions of softupdates is to order disk updates in such > > a way that the fs organizational integrity is maintained at all times. > > And we've recently found that this is simply not the case. The benefits > of SU are applicable to very specific environments; desktop PCs are the > main ones, offering great performance improvements there. Thanks for pointing that out. Is this an acknowledged bug in SU? Is it still a problem in 7.0? > > Of course this doesn't protect against actual sector corruption, but if > > the disk is between writes at the time it loses power, the fs structure > > is supposed to still be internally consistent. At least that's my > > understanding of it. > > Yep, that's how I understand it as well. But this is a different topic > than what we were discussing 2-3 replies ago, talking about how a RAID > controller with cache + BBU is sufficient enough to guarantee data > integrity even when power is lost -- that's incorrect. The reason I brought it up is that it occurred to me that if the hardware raid card reorders disk i/o it would mess with SU's ordering. I wonder whether this was happening in the previous thread you referred to concerning fsck? Rich
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