My boss basically wants RAID1 with all drives able to be read from. He has a requirement to have all the drives identical (minus the superblock) hence the 'near' option being used. From my rudimentary tests, sequential reds do seem to use all drives, but random reads don't. I wonder what logic is preventing the spreading out of random workloads for 'near'. 'far' is using all disks in random read and getting better performance on both random and sequential. I'm testing loopbacks on an NVME drive so seek latency should not be a major concern. ---------------- Robert LeBlanc PGP Fingerprint 79A2 9CA4 6CC4 45DD A904 C70E E654 3BB2 FA62 B9F1 On Wed, Nov 2, 2016 at 12:19 PM, <keld@xxxxxxxxxx> wrote: > There is some speed limits om raid10,n2 as also reported in > https://raid.wiki.kernel.org/index.php/Performance > > f you want speed, I suggest you use raid10,f2. > > Unfortunatlely you cannot grow "far" layouts, Neil says it is too complicated. > > But in your case you should be able to disable one of your raid10,N2 drives, > then build a raid10,n2 array for 3 disks, but only with the disk you removed from > your N2 disk plus your new disk. Then you can copy the contents of the remaining > old disk to the new "far" disk, and when complete, add the old raid10,n2 disk to the > new Far raid, with 3 disks. This should give you about 3 times the speed > of your old raid10,n2 array. > > Best regards > keld > > > > On Wed, Nov 02, 2016 at 11:59:25AM -0600, Robert LeBlanc wrote: >> We would like to add read performance to our RAID10 volume by adding >> another drive (we don't care about space), so I did the following test >> with poor results. >> >> # mdadm --create /dev/md13 --level 10 --run --assume-clean -p n2 >> --raid-devices 2 /dev/loop{2..3} >> mdadm: /dev/loop2 appears to be part of a raid array: >> level=raid10 devices=3 ctime=Wed Nov 2 11:25:22 2016 >> mdadm: /dev/loop3 appears to be part of a raid array: >> level=raid10 devices=3 ctime=Wed Nov 2 11:25:22 2016 >> mdadm: Defaulting to version 1.2 metadata >> mdadm: array /dev/md13 started. >> >> # mdadm --detail /dev/md13 >> /dev/md13: >> Version : 1.2 >> Creation Time : Wed Nov 2 11:47:48 2016 >> Raid Level : raid10 >> Array Size : 10477568 (9.99 GiB 10.73 GB) >> Used Dev Size : 10477568 (9.99 GiB 10.73 GB) >> Raid Devices : 2 >> Total Devices : 2 >> Persistence : Superblock is persistent >> >> Update Time : Wed Nov 2 11:47:48 2016 >> State : clean >> Active Devices : 2 >> Working Devices : 2 >> Failed Devices : 0 >> Spare Devices : 0 >> >> Layout : near=2 >> Chunk Size : 512K >> >> Name : rleblanc-pc:13 (local to host rleblanc-pc) >> UUID : 1eb66d7c:21308453:1e731c8b:1c43dd55 >> Events : 0 >> >> Number Major Minor RaidDevice State >> 0 7 2 0 active sync set-A /dev/loop2 >> 1 7 3 1 active sync set-B /dev/loop3 >> >> # mdadm /dev/md13 -a /dev/loop4 >> mdadm: added /dev/loop4 >> >> # mdadm --detail /dev/md13 >> /dev/md13: >> Version : 1.2 >> Creation Time : Wed Nov 2 11:47:48 2016 >> Raid Level : raid10 >> Array Size : 10477568 (9.99 GiB 10.73 GB) >> Used Dev Size : 10477568 (9.99 GiB 10.73 GB) >> Raid Devices : 2 >> Total Devices : 3 >> Persistence : Superblock is persistent >> >> Update Time : Wed Nov 2 11:48:13 2016 >> State : clean >> Active Devices : 2 >> Working Devices : 3 >> Failed Devices : 0 >> Spare Devices : 1 >> >> Layout : near=2 >> Chunk Size : 512K >> >> Name : rleblanc-pc:13 (local to host rleblanc-pc) >> UUID : 1eb66d7c:21308453:1e731c8b:1c43dd55 >> Events : 1 >> >> Number Major Minor RaidDevice State >> 0 7 2 0 active sync set-A /dev/loop2 >> 1 7 3 1 active sync set-B /dev/loop3 >> >> 2 7 4 - spare /dev/loop4 >> >> # mdadm --grow /dev/md13 -p n3 --raid-devices 3 >> mdadm: Cannot change number of copies when reshaping RAID10 >> >> I also tried to add the device, grow raid-devices, let it reshape, >> then try to change the number of copies and it didn't like that >> either. It would be nice to supply -p nX and --raid-devices X at the >> same time to prevent the reshape and only copy the data over to the >> new drive (or drop a drive out completely). I could see changing -p >> separately or at a different rate of drives added/removed could be >> difficult, but for lockstep changes, it seems that it would be rather >> easy. >> >> Any ideas? >> >> Thanks, >> >> ---------------- >> Robert LeBlanc >> PGP Fingerprint 79A2 9CA4 6CC4 45DD A904 C70E E654 3BB2 FA62 B9F1 >> -- >> 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
