On Mon 2009-08-24 16:22:22, Zan Lynx wrote: > Ric Wheeler wrote: >> Pavel Machek wrote: >>> Degraded MD RAID5 does not work by design; whole stripe will be >>> damaged on powerfail or reset or kernel bug, and ext3 can not cope >>> with that kind of damage. [I don't see why statistics should be >>> neccessary for that; the same way we don't need statistics to see that >>> ext2 needs fsck after powerfail.] >>> Pavel >>> >> What you are describing is a double failure and RAID5 is not double >> failure tolerant regardless of the file system type.... > > Are you sure he isn't talking about how RAID must write all the data > chunks to make a complete stripe and if there is a power-loss, some of > the chunks may be written and some may not? > > As I read Pavel's point he is saying that the incomplete write can be > detected by the incorrect parity chunk, but degraded RAID-5 has no > working parity chunk so the incomplete write would go undetected. Yep. > I know this is a RAID failure mode. However, I actually thought this was > a problem even for a intact RAID-5. AFAIK, RAID-5 does not generally > read the complete stripe and perform verification unless that is > requested, because doing so would hurt performance and lose the entire > point of the RAID-5 rotating parity blocks. Not sure; is not RAID expected to verify the array after unclean shutdown? 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
