On Tue, 10 May 2011 20:38:11 -0400 Dylan Distasio <interzone@xxxxxxxxx> wrote: > Hi Neil- > > Just out of curiosity, how does mdadm decide which layout to use on a > reshape from RAID5->6. I converted two of my RAID5s on different > boxes running the same OS awhile ago, and was not aware of the > different possibilities. When I check now, one of them was converted > with the Q block all on the last disk, and the other appears > normalized. I'm relatively confident I ran exactly the same command > on both to reshape them within a short time of one another. mdadm first converts the RAID5 to RAID6 in an instant atomic operation which results in the "-6" layout. It then starts a restriping process which converts the layout. If you end up with a -6 layout then something when wrong starting the restriping process. Maybe you used different version of mdadm? There have probably been bugs in some versions.. NeilBrown > > Here are the current details of the two arrays: > > dylan@terrordome:~$ sudo mdadm -D /dev/md0 > /dev/md0: > Version : 0.90 > Creation Time : Tue Mar 3 23:41:24 2009 > Raid Level : raid6 > Array Size : 5860559616 (5589.07 GiB 6001.21 GB) > Used Dev Size : 976759936 (931.51 GiB 1000.20 GB) > Raid Devices : 8 > Total Devices : 8 > Preferred Minor : 0 > Persistence : Superblock is persistent > > Intent Bitmap : Internal > > Update Time : Tue May 10 20:06:42 2011 > State : active > Active Devices : 8 > Working Devices : 8 > Failed Devices : 0 > Spare Devices : 0 > > Layout : left-symmetric-6 > Chunk Size : 64K > > UUID : 4891e7c1:5d7ec244:a9bd8edb: > d35467d0 (local to host terrordome) > Events : 0.743956 > > Number Major Minor RaidDevice State > 0 8 33 0 active sync /dev/sdc1 > 1 8 49 1 active sync /dev/sdd1 > 2 8 97 2 active sync /dev/sdg1 > 3 8 113 3 active sync /dev/sdh1 > 4 8 17 4 active sync /dev/sdb1 > 5 8 65 5 active sync /dev/sde1 > 6 8 241 6 active sync /dev/sdp1 > 7 65 17 7 active sync /dev/sdr1 > dylan@terrordome:~$ lsb_release -a > No LSB modules are available. > Distributor ID: Ubuntu > Description: Ubuntu 10.04.1 LTS > Release: 10.04 > Codename: lucid > > > dylan@rapture:~$ sudo mdadm -D /dev/md0 > > /dev/md0: > Version : 0.90 > Creation Time : Sat Jun 7 02:54:05 2008 > Raid Level : raid6 > Array Size : 2194342080 (2092.69 GiB 2247.01 GB) > Used Dev Size : 731447360 (697.56 GiB 749.00 GB) > Raid Devices : 5 > Total Devices : 5 > Preferred Minor : 0 > Persistence : Superblock is persistent > > Update Time : Tue May 10 20:19:13 2011 > State : clean > Active Devices : 5 > Working Devices : 5 > Failed Devices : 0 > Spare Devices : 0 > > Layout : left-symmetric > Chunk Size : 64K > > UUID : 83b4a7df:1d05f5fd:e368bf24:bd0fce41 > Events : 0.723556 > > Number Major Minor RaidDevice State > 0 8 18 0 active sync /dev/sdb2 > 1 8 34 1 active sync /dev/sdc2 > 2 8 2 2 active sync /dev/sda2 > 3 8 66 3 active sync /dev/sde2 > 4 8 82 4 active sync /dev/sdf2 > > dylan@rapture:~$ lsb_release -a > No LSB modules are available. > Distributor ID: Ubuntu > Description: Ubuntu 10.04.1 LTS > Release: 10.04 > Codename: lucid > > On Tue, May 10, 2011 at 8:21 PM, NeilBrown <neilb@xxxxxxx> wrote: > > > > On Wed, 11 May 2011 09:39:27 +1000 Steven Haigh <netwiz@xxxxxxxxx> wrote: > > > > > On 11/05/2011 9:31 AM, NeilBrown wrote: > > > > When it finished you will have a perfectly functional RAID6 array with full > > > > redundancy. It might perform slightly differently to a standard layout - > > > > I've never performed any measurements to see how differently. > > > > > > > > If you want to (after the recovery completes) you could convert to a regular > > > > RAID6 with > > > > mdadm -G /dev/md0 --layout=normalise --backup=/some/file/on/a/different/device > > > > > > > > but you probably don't have to. > > > > > > > > > > This makes me wonder. How can one tell if the layout is 'normal' or with > > > Q blocks on a single device? > > > > > > I recently changed my array from RAID5->6. Mine created a backup file > > > and took just under 40 hours for 4 x 1Tb devices. I assume that this > > > means that data was reorganised to the standard RAID6 style? The > > > conversion was done at about 4-6Mb/sec. > > > > Probably. > > > > What is the 'layout' reported by "mdadm -D"? > > If it ends -6, then it is a RAID5 layout with the Q block all on the last > > disk. > > If not, then it is already normalised. > > > > > > > > Is there any effect on doing a --layout=normalise if the above happened? > > > > > Probably not. > > > > NeilBrown > > > > -- > > 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 -- 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
