Date: Mon, 8 Nov 2010 22:44:17 +0000 From: krad <kraduk@gmail.com> To: Roland Smith <rsmith@xs4all.nl> Cc: "Svein Skogen \(Listmail account\)" <svein-listmail@stillbilde.net>, "C. P. Ghost" <cpghost@cordula.ws>, freebsd-questions@freebsd.org Subject: Re: ZFS License and Future Message-ID: <AANLkTiksMOBUiExkA%2B4Md9gbmZtgENYUBcYKk9cZVjR2@mail.gmail.com> In-Reply-To: <20101108223531.GA54089@slackbox.erewhon.net> References: <AANLkTi=dKatHYLFhC35VTT4fCAKgYLKEri2yVCPtSv7g@mail.gmail.com> <AANLkTinxLcrRoB6b2AcTrxHLqRCkyoWUhU=EmuvzEZQ8@mail.gmail.com> <20101106203016.GB13095@guilt.hydra> <20101106213836.GA77198@slackbox.erewhon.net> <AANLkTi=7MhvRTLP1NzGaHQFsV=FU8QDn5K73EmLPZH2k@mail.gmail.com> <4CD8194D.7080208@qeng-ho.org> <4CD82081.50309@stillbilde.net> <20101108183821.GA48373@slackbox.erewhon.net> <AANLkTikcCFr4GttjNrq9Kxxz1pyZbPc82BsJ6a3siw5t@mail.gmail.com> <20101108223531.GA54089@slackbox.erewhon.net>
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On 8 November 2010 22:35, Roland Smith <rsmith@xs4all.nl> wrote: > On Mon, Nov 08, 2010 at 09:44:29PM +0100, C. P. Ghost wrote: > > On Mon, Nov 8, 2010 at 7:38 PM, Roland Smith <rsmith@xs4all.nl> wrote: > > > On Mon, Nov 08, 2010 at 05:08:33PM +0100, Svein Skogen (Listmail > account) wrote: > > >> But it's still not capable of true forward-error-correction. If we are > > >> to embark upon creating a new solution, using something that is cheap > > >> for "normal cases" but can still be used (albeit more expensively) for > > >> error recovery would (imho) be better. Even if that means we get less > > >> net storage out of the gross pool (it could perhaps be configurable?) > > > > > > I'm not sure what you mean by "true forward-error-correction". But if > you want > > > to make _really sure_ that a spinning disk hasn't mangled the data you > should: > > > > Maybe something like Reed-Solomon ECC in different blocks. > > Should a data block go bad, it could be rebuilt on-the-fly from > > those ECC blocks: > > And how do you detect that a block has gone bad, other than reading back > what > you wrote and finding a difference? Because that would still be slow. > > Roland > -y > R.F.Smith http://www.xs4all.nl/~rsmith/<http://www.xs4all.nl/%7Ersmith/>; > [plain text _non-HTML_ PGP/GnuPG encrypted/signed email much appreciated] > pgp: 1A2B 477F 9970 BA3C 2914 B7CE 1277 EFB0 C321 A725 (KeyID: C321A725) > The read doesnt need to be done at write time, it only needs to be done when the block is read by the system. If an issue is found than the corrective measures are executed. For you important data in my opinion you should always set the copies attribute to 3. This is obviously very costly in terms of storage but its just a trade off for the data.
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