Clinton Lee Taylor wrote: > Greetings ... > > 2009/9/2 Bill Davidsen <davidsen@xxxxxxx>: > >> Clinton Lee Taylor wrote: >> >>> http://www.issociate.de/board/post/498227/Ext3_convert_to_RAID1_....html >>> >>> Wanting to convert an already created and populated ext3 filesystem. >>> >>> I unmounted the filesystem, ran e2fsck -f /dev/sdb1 to check that the >>> current filesystem had no errors. >>> Then ran mdadm --create /dev/md0 --level=1 -n 1 /dev/sdb1 --force to >>> create the RAID1 device, answered yes to the question. >>> >>> >> Right here is where you invite problems. >> > This just a warning or have you had problems doing this? > > > If you don't remember to shrink the filesystem you lose data. The list > has had tales of woe from people who have done it. I personally > haven't. Oh, and shrinking a filesystem is not totally without > possibility of having problems due to hardware or power issues or even > just a crash. > > > Doing it the other way avoids this, all failures keep the original data safe. > > - create an array using the NEW partition > - make the filesystem on the new array > - mount the new filesystem > - copy the data to the new array and verify > - umount the old partition > - mount the array on the OLD mount point > - add the OLD partition to the array and let the system refresh it >> You want to create the array using >> the new device or partition, and put a new filesystem on it. >> > No, I want to convert an existing ext3 to RAID1 partition ... > See above, you want to wind up with the data on an array, preferably without modifying the old data until the old data has been moved and verified. > >> Read and >> understand the man page for mke2fs in the stride= and stripe-width= >> parameters, it shouldn't matter for raid-1 but would if you use raid-[56]. >> > How would striding effect RAID growing or shrinking? Does not the > striding just effect performance or is it a big problem? Would a RAID > defragger help? > > On raid-[456] it can improve performance. I mentioned it because people overlook it. And if I were doing this I would use raid-10 to get better performance, but that's me. >> Then mount the array, copy the data to the array, verify it, and then >> unmount the old partition and add it. >> > I know this is a tried, tested and accept procedure to > transfer/transform an existing ext3 partition to a RAID partition, but > this takes allot of data coping and requires double extra storage ... > You are going to use the NEW partition as part of the array anyway, it takes no extra storage. > What I'm trying to get right, is to create and test a procedure ( with > audience help and peer review ), to convert an ext3 partition to a > RAID1, maybe later other RAID, but this is a first step/test ... > > Using a missing disk component should work with any raid level but raid-0. ;-) >>> Ran e2fsck -v /dev/md0 to check that the RAID1 device had no >>> filesystem corruption on it, which it did not. >>> Added a spared RAID device using mdadm --add /dev/md0 /dev/sdc1 >>> Then grew the RAID1 device to two compents with mdadm --grow /dev/md0 >>> --raid-disks=2 --backup-file=/root/raid1.backup.file >>> >> I have an entry in my raid notes which says that's the wrong thing to do, >> the array should be created with the correct number of members and one left >> "missing" to be added later. My note says it should be done that way, but >> not why it's better, but it says "per Neil" so I bet there is a reason. It >> does seem to work that way, I just did an adventure in file moving to test >> it the hard way. I was doing a mix of raid-1, raid-10, and raid-5 arrays >> moving from little drives (750GB) to larger ones. >> > Okay, but now we have a big question, creating RAID MD with less > devices than they should have should only be done with "missing" or > forced with number of devices? Could the really Neil stand up now? > ;-) > > I'd like to hear at this point, too. I don't want to modify the old partition until the new one is working, other than being paranoid is there a downside to that? >>> Did another filesystem check once the RAID finished rebuilding and all >>> seemed fine. >>> Double checked that the data on the RAID was the same as the original >>> data by diffing the two, again all was fine. >>> >>> Now is this just lucky or would this be an acceptable way to convert >>> an existing ext3 filesystem to RAID1? >>> >> See above, given the resize you didn't mention it's okay, but forget the >> resize and you risk your data. >> > Okay, so, you saying that I should make sure that I shrink the ext3 > before try and convert, which is what was comment on before ... I only > edited out what I thought was not needed for the basic question of > converting, but, when I write up an article covering this, I will be > sure to detail that and explain that md metadata version 0.90 puts > it's metadata at the end of the device, which should be free, after > the shrink ... > -- bill davidsen <davidsen@xxxxxxx> CTO TMR Associates, Inc "Now we have another quarterback besides Kurt Warner telling us during postgame interviews that he owes every great thing that happens to him on a football field to his faith in Jesus. I knew there had to be a reason why the Almighty included a mute button on my remote." -- Arthur Troyer on Tim Tebow (Sports Illustrated) -- 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
