On Fri, 03 Dec 2010 00:49:52 -0800 Phil Karn <karn@xxxxxxxx> wrote: > Are there any papers documenting the implementation of the Linux RAID > subsystem? I'm interested in some of the details of how RAID-5 works. I would suggest man mdadm and man md That should answer at least some of your questions. Then try http://raid.wiki.kernel.org/ If you have further questions after that, please ask. NeilBrown > > I've never seen a virgin disk drive from the factory that wasn't all > 0's. Creating a RAID array on a set of such drives triggers an initial > rebuild that simply writes lots zeroes on lots of zeroes. With disks now > pushing past 2 TB, this can easily take half a day. > > Except for the admittedly somewhat useful side effect of scanning the > disks for bad sectors, all this activity seems rather unnecessary. Is > there a way to create a RAID-5 (or any other RAID level) array so that > it will immediately come up without an initial rebuild? > > File systems generally don't read disk blocks that they haven't already > written. So even when you build a RAID array from drives with old data, > I can't see how skipping the initial rebuild can cause any real harm. > The first write to any block causes the RAID system to initialize the > parity in that stripe, thus making it possible to regenerate that block > in case of a drive failure. > > During the initial rebuild of a RAID-5 array, /proc/mdstat suggests that > the array is operating in degraded mode and the last drive in the array > is being rebuilt. Is this true, i.e., are all the rebuild writes going > to that last drive? > > How does a rebuilding RAID-5 array handle a read or write operation when > it lands on the "broken" drive? Does it depend on whether the block is > before or after the rebuild pointer? > > Thanks much, > > Phil > -- > To unsubscribe from this list: send the line "unsubscribe linux-raid" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
