Date: Fri, 19 Aug 2011 17:51:02 -0700 From: Kevin Oberman <kob6558@gmail.com> To: Dan Langille <dan@langille.org> Cc: freebsd-stable@freebsd.org Subject: Re: bad sector in gmirror HDD Message-ID: <CAN6yY1vitKEiry1SGUv4gCe69mvXoqFOTYZn299cFKw%2BG1VS4g@mail.gmail.com> In-Reply-To: <20110819235719.GA64220@night.db.net> References: <1B4FC0D8-60E6-49DA-BC52-688052C4DA51@langille.org> <20110819235719.GA64220@night.db.net>
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On Fri, Aug 19, 2011 at 4:57 PM, Diane Bruce <db@db.net> wrote: > On Fri, Aug 19, 2011 at 04:50:01PM -0400, Dan Langille wrote: >> System in question: FreeBSD 8.2-STABLE #3: Thu Mar =A03 04:52:04 GMT 201= 1 >> >> After a recent power failure, I'm seeing this in my logs: >> >> Aug 19 20:36:34 bast smartd[1575]: Device: /dev/ad2, 2 Currently unreada= ble (pending) sectors >> > > Personally, I'd replace that drive now. > >> Searching on that error message, I was led to believe that identifying t= he bad sector and >> running dd to read it would cause the HDD to reallocate that bad block. > > No, as otherwise mentioned (Hi Jeremy!) you need to read and write the > block. This could buy you a few more days or a few more weeks. Personally= , > I would not wait. Your call. > While I largely agree, it depends on several factors as to whether I'd replace the drive. First, what does SMART show other then these errors? If the reported statistics look generally good, and considering that you a mirror with one "good" copy of the blocks in question, the impact is zero unless the other drive fails. That is why the blocks need to be re-written so that they will be re-located on the drive. Second, how critical is the data? The mirror gives good integrity, but you also need good backups. If the data MUST be on-line with high reliability, buy a replacement drive. You need to look at cost-benefit (or really the cost of replacement vs. cost of failure). It's worth mentioning that all drives have bad blocks. Most are hard bad blocks and are re-mapped before the drive is shipped, but marginal bad blocks can and do slip through to customers and it is entirely possible that the drive is just fine for the most part and replacing it is really a waste of money. Only you can make the call, but if further bad blocks show up in the near term, I'll go along with recommending replacement. --=20 R. Kevin Oberman, Network Engineer - Retired E-mail: kob6558@gmail.com
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