Date: Fri, 12 Dec 2003 09:29:22 -0600 From: Dan Nelson <dnelson@allantgroup.com> To: Dru <dlavigne6@sympatico.ca> Cc: questions@freebsd.org Subject: Re: dd of mounted filesystem Message-ID: <20031212152922.GP2435@dan.emsphone.com> In-Reply-To: <20031212084227.Q604@genisis.domain.org> References: <20031211145245.D637@genisis> <20031211201144.GD75256@happy-idiot-talk.infracaninophile.co.uk> <20031211202155.GK2435@dan.emsphone.com> <20031212084227.Q604@genisis.domain.org>
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In the last episode (Dec 12), Dru said: > On Thu, 11 Dec 2003, Dan Nelson wrote: > > In the last episode (Dec 11), Matthew Seaman said: > > > Remember that dd(1) traverses the block device sequentially, but > > > that most FS accesses are random, so any particular change can > > > span either side of dd(1)'s offset. Also that dd'ing from the > > > block device bypasses the usual machinery for doing file IO -- > > > machinery that is designed under the premise that it will have > > > sole control over what gets read or written where and when. > > > > On current you can get around the consistency problem by dd'ing a > > snapshot of the filesystem, just like dump's -L flag does. > > You mean, run "makesnap_ffs" first? I've been meaning to play with > that one, I'll have to try it out. I don't think that's a standard FreeBSD command; what I was thinking of was something like: mount -u -o snapshot /usr/.snap/snap1 /usr dd if=/usr/.snap/snap1 of=blah bs=64k rm /usr/.snap/snap1 -- Dan Nelson dnelson@allantgroup.com
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