Date: Wed, 17 Jul 2002 00:33:13 -0700 From: Peter Wemm <peter@wemm.org> To: "Mark W. Krentel" <krentel@dreamscape.com> Cc: freebsd-hackers@freebsd.org Subject: Re: dump on mounted fs Message-ID: <20020717073313.9C21D3910@overcee.wemm.org> In-Reply-To: <200207170529.g6H5Tr512665@dreamscape.com>
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"Mark W. Krentel" wrote: > Dump still works on a mounted file system in Freebsd, right? That is, > a write that completes before dump is started will be in the dump, > even if the data is in memory? I don't mean writing to a file during > the dump, that's a separate problem. > > I only recently learned that this doesn't work in Linux and I wanted > to check that it's (still?) ok in Freebsd. Apparently, in the 2.4 > Linux kernels, the buffer and page caches make it impossible for dump > to always get the correct version of a file, even if there are no > writes during the dump. It takes a umount before dump will see all of > the changes (yuck). > > Anyone know about Solaris, IRIX, etc? Dump on a live FS is always risky. FreeBSD in 4.x and earlier will have up to about a 30 second delay before a write() makes it to physical disk. However, 5.x have snapshots where you can take a virtual snapshot of the file system device as it existed at the instant that you create it. You can then take a coherent dump that *will* be accurate. fsck uses snapshots in 5.x to do background fsck to reclaim lost resources. 5.0 should be released sometime this century. :-) Cheers, -Peter -- Peter Wemm - peter@wemm.org; peter@FreeBSD.org; peter@yahoo-inc.com "All of this is for nothing if we don't go to the stars" - JMS/B5 To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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