On Mon, Mar 8, 2010 at 10:11 PM, Michael Evans <mjevans1983@xxxxxxxxx> wrote: > On Mon, Mar 8, 2010 at 1:04 PM, Mark Knecht <markknecht@xxxxxxxxx> wrote: >> On Mon, Mar 8, 2010 at 12:58 PM, Robin Hill <robin@xxxxxxxxxxxxxxx> wrote: >>> On Mon Mar 08, 2010 at 12:39:26PM -0800, Mark Knecht wrote: >>> >>>> Hi all, >>>> I'm still very much on a steep learning curve about what I can do >>>> with Linux software RAID. In another thread this weekend a couple of >>>> responders discussed among themselves 3-disk RAID1 solutions that can >>>> survive if 2 disks die. I don't understand what that means. Can >>>> someone point me at a quick explanation? Is that really possible? >>>> >>>> In general I'm using a few Wikipedia pages and gravitate toward the >>>> diagrams as much as anything. >>>> >>>> http://en.wikipedia.org/wiki/RAID >>>> http://en.wikipedia.org/wiki/RAID1#RAID_1 >>>> >>>> RAID0 - striping, speed not reliability (2 disk minimum) >>>> RAID1 - duplicate data, no other protection (2 disk minimum) >>>> >>>> How do I build RAID1 using three drives? Just duplicate the data 3 >>>> times? If drives start going bad how do I determine which one or two >>>> are failing? (fsck? SMART?) With 3 drives 1 fail seems relatively >>>> straightforward to figure out, but 2? >>>> >>> A 3-disk RAID1 is just 3 duplicate copies, yes. And RAID only protects >>> against hardware failures, so you know which disk has failed because it >>> gets kicked out of the array as faulty. This is the same regardless of >>> how many mirrored copies you have (md will detect a write failure to a >>> drive and mark it as faulty - read errors will cause the failed block to >>> get rewritten). >>> >>> As for how to create it - it's just the same process as for a 2-disk >>> RAID1 but specifying 3 drives (assuming you're using Linux md software >>> RAID - if not, please specify what you're intending to use). The manual >>> page for mdadm should give you everything you need - do ask if there's >>> anything you want clarifying though. >>> >>> Cheers, >>> Robin >> >> Thanks Robin. Maybe I am getting smarter about this if I'm figuring >> out what others are talking about! ;-) >> >> Cheers, >> Mark >> -- >> 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 >> > > When in doubt, read the manual two or three more times. > > This might also help you: http://wiki.tldp.org/LVM-on-RAID I wrote > some background comparison sections when I made that... Good advice. The contents of the manual didn't really stick for me until I'd actually *done* the tasks I was trying to figure out. The beautiful and classic Catch-22 of learning new things. So I somewhat empathically suggest you obtain a virtual machine program and start up a few disposable virtual machines. (VirtualBox is pretty good and also free.) Try creating some RAID's on VM's and getting them to boot, try failing a device and readding it, etc. And keep the manual in a window next to the virtual machine's window :) -- Kristleifur -- 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
