Date: Thu, 27 Apr 2006 09:13:33 -0500 From: Robert <robert@mhi-tx.com> To: anderson@centtech.com Cc: freebsd-fs@freebsd.org Subject: Re: suspend writes for external snapshot Message-ID: <4450D18D.9060101@mhi-tx.com> In-Reply-To: <4450B3B1.8070704@centtech.com> References: <444FE114.7010106@mhi-tx.com> <20060426211059.GA85780@xor.obsecurity.org> <4450B3B1.8070704@centtech.com>
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Eric Anderson wrote: > Kris Kennaway wrote: > >> On Wed, Apr 26, 2006 at 04:07:32PM -0500, Robert wrote: >> >>> Greetings, >>> I am trying to determine if there is a way to suspend write activity >>> on a FreeBSD filesystem (currently 6.0R) in order to take a snapshot >>> with external SAN software (Falconstor IPStor)? >> >> >> Use a FreeBSD snapshot and then image that? > > > He can't do it that way because the Falconstor is a raw block device and > has no idea the difference between a snapshot and other filesystem bits. > > > Robert - we have some very alpha patches in house that allow suspension > of UFS filesystems for things like this (also working on online UFS > growing). I'm not sure how close we really are to letting it loose in > the wild, but we will definitely be making all the patches available to > whomever wants it. > > > Eric > > > Sounds great thank you, I will keep an eye out for the patches. I am still unclear as to the necessity of suspending writes based on the following information from http://www.mckusick.com/softdep/ "By ensuring that the only inconsistencies are unclaimed blocks or inodes, soft updates can eliminate the need to run a filesystem check program after every system crash. Instead, the system is brought up immediately. When it is convenient, a snapshot is taken and a background task can be run on on that snapshot to reclaim any lost blocks and inodes. The use of a snapshot allows normal filesystem activity to continue concurrently. " Does this mean that I can take a snapshot of an in use filesystem and the only ill effects will be the lost blocks and inodes which can be reclaimed with background fsck once the snapshot is booted? Robert
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