I tried this on real hardware and it appears to work although it is abysmally slow:
vishvananda@nebstack006:~$ echo "0 2097152 zero" | sudo dmsetup create zero1 vishvananda@nebstack006:~$ echo "0 2097152 snapshot /dev/mapper/zero1 /dev/sde n 128" | sudo dmsetup create clean1 vishvananda@nebstack006:~$ sudo dd if=/dev/zero of=/dev/mapper/clean1 bs=1M count=1024 1024+0 records in 1024+0 records out 1073741824 bytes (1.1 GB) copied, 15.1229 s, 71.0 MB/s vishvananda@nebstack006:~$ time sudo dd if=/dev/zero of=/dev/mapper/clean1 bs=1M count=1024 1024+0 records in 1024+0 records out 1073741824 bytes (1.1 GB) copied, 8.03134 s, 134 MB/s real 0m8.041s user 0m0.004s sys 0m1.208s vishvananda@nebstack006:~$ time sudo dd if=/dev/zero of=/dev/sde bs=1M count=1024 1024+0 records in 1024+0 records out 1073741824 bytes (1.1 GB) copied, 0.666776 s, 1.6 GB/s real 0m0.677s user 0m0.000s sys 0m0.668s vishvananda@nebstack006:~$ cat /sys/block/sde/queue/scheduler noop deadline [cfq] vishvananda@nebstack006:~$ echo deadline | sudo tee /sys/block/sde/queue/scheduler deadline vishvananda@nebstack006:~$ cat /sys/block/sde/queue/scheduler noop [deadline] cfq vishvananda@nebstack006:~$ time sudo dd if=/dev/zero of=/dev/sde bs=1M count=1024 1024+0 records in 1024+0 records out 1073741824 bytes (1.1 GB) copied, 0.503988 s, 2.1 GB/s real 0m0.513s user 0m0.004s sys 0m0.504s vishvananda@nebstack006:~$ time sudo dd if=/dev/zero of=/dev/mapper/clean1 bs=1M count=1024 1024+0 records in 1024+0 records out 1073741824 bytes (1.1 GB) copied, 11.316 s, 94.9 MB/s real 0m11.327s user 0m0.000s sys 0m1.184s going to try the same on quantal to see how it looks. -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1023755 Title: Precise kernel locks up while dd to /dev/mapper files > 1Gb (was: Unable to delete volume) To manage notifications about this bug go to: https://bugs.launchpad.net/cinder/+bug/1023755/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
