Date: Tue, 23 Jan 2007 12:00:56 -0700 From: Reed Loefgren <reedl@tatteredcover.com> To: freebsd-geom@FreeBSD.ORG, fernan.aguero@gmail.com Subject: Re: clear metadata using dd? Message-ID: <45B65B68.5040209@tatteredcover.com> In-Reply-To: <200701231830.l0NIURmC083278@lurza.secnetix.de> References: <200701231830.l0NIURmC083278@lurza.secnetix.de>
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Oliver Fromme wrote: > Hi, > > I just noticed this message today, and there's one thing > I don't understand ... > > Fernan Aguero wrote: > > I'm trying to set up two disks to contain both gmirrored and > > gstriped slices. > > > > This is what I'm trying to achieve: > > adxs1, swap > > adxs2, gmirror > > adxs3, gstripe > > Can someone please explain why such a setup makes sense? > > As far as I can tell, the purpose of gmirror is to provide > redundancy in the case of drive failure. I.e. if one > drive fails, the system keeps running happily instead of > crashing. > > But if only part of the disk is mirrored, then the system > will still crash if one drive fails. So what is the point > of using gmirror, if not on whole disks? > > Just wondering. > > Best regards > Oliver > > Oliver, I have gmirror running on my home machine; the entire disk mirrored to a second disk, swap included, because that was the setup I followed on onlamp's BSD section. In retrospect I would not mirror swap since writing to a mirrored swap is a performance hit that might not be compensated by the increased read performance of mirrors. I see swap as both already slow (compared to RAM) but also somewhat disposable. If I were to do it again I would mirror the entire slice (DOS partition) holding the OS but leave two slices with the swap partitions on them independent, mount both of them with identical priorities, and let the OS determine the best usage algorithm. I have a gig of RAM and only rarely even touch swap, plus my career doesn't hang on such decisions so I can afford to play a bit. Your situation might not have that leeway. :) r
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