On Tue 2009-08-25 17:20:13, david@xxxxxxx wrote: > On Wed, 26 Aug 2009, Pavel Machek wrote: > >> On Tue 2009-08-25 16:56:40, david@xxxxxxx wrote: >>> On Wed, 26 Aug 2009, Pavel Machek wrote: >>> >>>> There are storage devices that high highly undesirable properties >>>> when they are disconnected or suffer power failures while writes are >>>> in progress; such devices include flash devices and MD RAID 4/5/6 >>>> arrays. >>> >>> change this to say 'degraded MD RAID 4/5/6 arrays' >>> >>> also find out if DM RAID 4/5/6 arrays suffer the same problem (I strongly >>> suspect that they do) >> >> I changed it to say MD/DM. >> >>> then you need to add a note that if the array becomes degraded before a >>> scrub cycle happens previously hidden damage (that would have been >>> repaired by the scrub) can surface. >> >> I'd prefer not to talk about scrubing and such details here. Better >> leave warning here and point to MD documentation. > > I disagree with that, the way you are wording this makes it sound as if > raid isn't worth it. if you are going to say that raid is risky you need > to properly specify when it is risky Ok, would this help? I don't really want to go to scrubbing details. (*) Degraded array or single disk failure "near" the powerfail is neccessary for this property of RAID arrays to bite. >>>> THESE devices have the property of potentially corrupting blocks being >>>> written at the time of the power failure, >>> >>> this is true of all devices >> >> Actually I don't think so. I believe SATA disks do not corrupt even >> the sector they are writing to -- they just have big enough >> capacitors. And yes I believe ext3 depends on that. > > you are incorrect on this. > > ext3 (like every other filesystem) just accepts the risk (zfs makes some > attempt to detect such corruption) I'd like Ted to comment on this. He wrote the original document, and I'd prefer not to introduce mistakes. 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-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
