fsck more often when powerfail is detected (was Re: wishful thinking about atomic, multi-sector or full MD stripe width, writes in storage)
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From: Pavel Machek on 4 Apr 2010 09:50 Hi! > > Yes, but ext3 was designed to handle the partial write (according to > > tytso). > > I'm not sure what made you think that I said that. In practice things > usually work out, as a conseuqence of the fact that ext3 uses physical > block journaling, but it's not perfect, becase... Ok; so the journalling actually is not reliable on many machines -- not even disk drive manufacturers guarantee full block writes AFAICT. Maybe there's time to reviwe the patch to increase mount count by >1 when journal is replayed, to do fsck more often when powerfails are present? > > > Also, when you enable the write cache (MD or not) you are buffering > > > multiple MB's of data that can go away on power loss. Far greater (10x) > > > the exposure that the partial RAID rewrite case worries about. > > > > Yes, that's what barriers are for. Except that they are not there on > > MD0/MD5/MD6. They actually work on local sata drives... > > Yes, but ext3 does not enable barriers by default (the patch has been > submitted but akpm has balked because he doesn't like the performance > degredation and doesn't believe that Chris Mason's "workload of doom" > is a common case). Note though that it is possible for dirty blocks > to remain in the track buffer for *minutes* without being written to > spinning rust platters without a barrier. So we do wrong thing by default. Another reason to do fsck more often when powerfails are present? Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |