Date: Thu, 27 Apr 2006 09:17:28 -0500 From: Eric Anderson <anderson@centtech.com> To: Robert <robert@mhi-tx.com> Cc: freebsd-fs@freebsd.org Subject: Re: suspend writes for external snapshot Message-ID: <4450D278.5000802@centtech.com> In-Reply-To: <4450D18D.9060101@mhi-tx.com> References: <444FE114.7010106@mhi-tx.com> <20060426211059.GA85780@xor.obsecurity.org> <4450B3B1.8070704@centtech.com> <4450D18D.9060101@mhi-tx.com>
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Robert wrote: > 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? I believe so, yes. Someone correct me here if I am wrong. Eric -- ------------------------------------------------------------------------ Eric Anderson Sr. Systems Administrator Centaur Technology Anything that works is better than anything that doesn't. ------------------------------------------------------------------------
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