On 02/01/2016 05:53 AM, Bob Gustafson wrote: > Description of problem: > > I am trying to copy /root, /home from a single disk (running the os) to a > bigger raid 1 disk pair running in the same chassis. > > fedora is the lvm vg_group of the running system, fedora23 is the lvm > vg_group of the new disks (raid 1, 2TB disks). > > [root@hoho8-chidig-com user1]# lvscan > ACTIVE '/dev/fedora/swap' [15.57 GiB] inherit > ACTIVE '/dev/fedora/home' [865.45 GiB] inherit > ACTIVE '/dev/fedora/root' [50.00 GiB] inherit > ACTIVE '/dev/fedora23/swap' [15.60 GiB] inherit > ACTIVE '/dev/fedora23/root' [50.00 GiB] inherit > ACTIVE '/dev/fedora23/home' [1.75 TiB] inherit > > > Below is the command I'm using to copy over one partition to the raid pair: > > [root@hoho8-chidig-com user1]# dd if=/dev/fedora/root of=/dev/fedora23/root > 104857600+0 records in > 104857600+0 records out > 53687091200 bytes (54 GB) copied, 5639.3 s, 9.5 MB/s > [root@hoho8-chidig-com user1]# > > > [root@hoho8-chidig-com user1]# df -h > Filesystem Size Used Avail Use% Mounted on > devtmpfs 16G 0 16G 0% /dev > tmpfs 16G 392K 16G 1% /dev/shm > tmpfs 16G 1.8M 16G 1% /run > tmpfs 16G 0 16G 0% /sys/fs/cgroup > /dev/mapper/fedora-root 50G 27G 20G 58% / > tmpfs 16G 84K 16G 1% /tmp > /dev/loop0 1.9G 3.0M 1.7G 1% /srv/node/swift_loopback > /dev/mapper/fedora-home 852G 57G 752G 7% /home > /dev/sdc1 477M 215M 233M 48% /boot > tmpfs 3.2G 8.0K 3.2G 1% /run/user/42 > tmpfs 3.2G 24K 3.2G 1% /run/user/1000 > > Note that dd says 54GB were copied over into a disk partition of size only > 50GB. No errors during the copy. And the results show that only 27G was in > the fedora partition to start with. (54GB is double 27GB - this may be a clue) > > Another example: > > [root@hoho8-chidig-com user1]# dd if=/dev/fedora/home of=/dev/fedora23/home > 1814978560+0 records in > 1814978560+0 records out > 929269022720 bytes (929 GB) copied, 32437.8 s, 28.6 MB/s > [root@hoho8-chidig-com user1]# > > Taking a look at the data size on the target partitions: > > [root@hoho8-chidig-com user1]# mount /dev/fedora23/root /mnt/rootn > [root@hoho8-chidig-com user1]# mount /dev/fedora23/home /mnt/homen > > [root@hoho8-chidig-com user1]# du -h /mnt/rootn | tail -1 > 26G /mnt/rootn > > [root@hoho8-chidig-com user1]# du -h /mnt/homen | tail -1 > 57G /mnt/homen > > for the rootn partition, the 26G copied size is consistent with the source > size. > > For the homen partition, the 57G is consistent with the source size. > > However, the count given by the dd copies don't match: > > In the case of the root->rootn copy it is 54G instead of 27G > in the case of the home->homen copy it is 942G instead of 57G > > > Version-Release number of selected component (if applicable): > > dd is (coreutils) 8.24 > > How reproducible: > > I did two tests - as shown > > Steps to Reproduce: > 1. create raid 1 pair > 2. copy a 3rd single disk partition to a raid1 pair lvm partition > 3. do df and compare results. > > Actual results: > > As shown above in problem narative. > > Expected results: > > I would think that the sizes reported by dd and df would be comparable, but > they are not. > > Additional info: > > See also https://bugzilla.redhat.com/show_bug.cgi?id=1303456
I think there are several misunderstandings here ... which is like comparing apples and oranges. a) the MiB numbers are 1024-based, while MB are 1000-based. b) df(1) and du(1) show statistics or summaries of the data *inside* a file system, while the file system itself may need some space to manage the data. And even df/du report different sizes: http://www.gnu.org/software/coreutils/faq/coreutils-faq.html#df-and-du-report-different-information Starting with BTRFS, the situation may even be worse (df showing lots of free space while BTRFS doesn't allow to create - or even delete - another file). Thus said: the size of the underlying device is not 100% related to the sizes inside the file system on that device. You may get the real size using e.g. $ wc -c < /dev/sda1 2147483648 and dd(1) will report the same size: $ dd if=/dev/sda1 of=/dev/null 4194304+0 records in 4194304+0 records out 2147483648 bytes (2.1 GB) copied, 1.54335 s, 1.4 GB/s Have a nice day, Berny
