From mboxrd@z Thu Jan 1 00:00:00 1970 From: Justin Piszcz Subject: Re: Software RAID when it works and when it doesn't Date: Fri, 26 Oct 2007 12:11:47 -0400 (EDT) Message-ID: References: <14526.1192571833@mdt.ecitele.com> <87bqaw5tqb.fsf@informatik.uni-tuebingen.de> <1192777672.16416.495.camel@w100> <87k5p9zwip.fsf@informatik.uni-tuebingen.de> Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed Return-path: In-Reply-To: <87k5p9zwip.fsf@informatik.uni-tuebingen.de> Sender: linux-raid-owner@vger.kernel.org To: Goswin von Brederlow Cc: Alberto Alonso , Mike Accetta , Neil Brown , linux-raid@vger.kernel.org List-Id: linux-raid.ids On Fri, 26 Oct 2007, Goswin von Brederlow wrote: > Justin Piszcz writes: > >> On Fri, 19 Oct 2007, Alberto Alonso wrote: >> >>> On Thu, 2007-10-18 at 17:26 +0200, Goswin von Brederlow wrote: >>>> Mike Accetta writes: >>> >>>> What I would like to see is a timeout driven fallback mechanism. If >>>> one mirror does not return the requested data within a certain time >>>> (say 1 second) then the request should be duplicated on the other >>>> mirror. If the first mirror later unchokes then it remains in the >>>> raid, if it fails it gets removed. But (at least reads) should not >>>> have to wait for that process. >>>> >>>> Even better would be if some write delay could also be used. The still >>>> working mirror would get an increase in its serial (so on reboot you >>>> know one disk is newer). If the choking mirror unchokes then it can >>>> write back all the delayed data and also increase its serial to >>>> match. Otherwise it gets really failed. But you might have to use >>>> bitmaps for this or the cache size would limit its usefullnes. >>>> >>>> MfG >>>> Goswin >>> >>> I think a timeout on both: reads and writes is a must. Basically I >>> believe that all problems that I've encountered issues using software >>> raid would have been resolved by using a timeout within the md code. >>> >>> This will keep a server from crashing/hanging when the underlying >>> driver doesn't properly handle hard drive problems. MD can be >>> smarter than the "dumb" drivers. >>> >>> Just my thoughts though, as I've never got an answer as to whether or >>> not md can implement its own timeouts. >>> >>> Alberto >>> >>> >>> - >>> To unsubscribe from this list: send the line "unsubscribe linux-raid" in >>> the body of a message to majordomo@vger.kernel.org >>> More majordomo info at http://vger.kernel.org/majordomo-info.html >>> >> >> I have a question with re-mapping sectors, can software raid be as >> efficient or good at remapping bad sectors as an external raid >> controller for, e.g., raid 10 or raid5? >> >> Justin. > > Software raid makes no remapping of bad sectors at all. It assumes the > disks will do sufficient remapping. > > MfG > Goswin > Thanks, this is what I was looking for. Justin.