See fdisk#Backup and restore partition table or gdisk#Backup and restore partition table.īoot from a live medium and make sure no partitions are mounted from the source hard drive. To notify of changes without rebooting, use a utility like partprobe (part of GNU Parted).

Partition table changes from dd are not registered by the kernel.

For swap partitions, use mkswap /dev/sd XY instead.

To regain unique UUIDs of an ext2/3/4 filesystem, use tune2fs /dev/sd XY -U random on every partition.

a single 512-byte read error will mess up the whole 64 KiB output block. But keep in mind that read errors on the source disk will end up as block errors on the destination disk, i.e. For example, changing bs from 512 to 64K changed copying speed from 35 MB/s to 120 MB/s on a simple Celeron 2.7 GHz system. If you are positive that your disk does not contain any errors, you could proceed using a larger block size, which will increase the speed of your copying several fold. This means, for a disk, that effectively the whole 1 MiB would become messed up because of a single 512 byte read error in the beginning of the read: 12ERROR89 would become 128900000 instead of 120000089. dd will, according to documentation, fill up the OBS to IBS size after completing its read, which means adding zeroes at the end of the block. Many people seem to think that dd will 'fill up read errors with zeroes' if you use the noerror,sync options, but this is not what happens. But if a read error occurs, things will go wrong. Normally, if your block size is, say, 1 MiB, dd will read 1024×1024 bytes and write as many bytes. When you set bs, you effectively set both IBS and OBS.

The dd utility technically has an 'input block size' (IBS) and an 'output block size' (OBS). Note: The block size you specify influences how read errors are handled. status=progress shows periodic transfer statistics which can be used to estimate when the operation may be complete.sync fills input blocks with zeroes if there were any read errors, so data offsets stay in sync.Default behavior for dd is to halt at any error. noerror instructs dd to continue operation, ignoring all read errors.See and for details and to figure out the best bs value for your use case. Also, please read the warning below, because there is more to this than just 'block sizes' -it also influences how read errors propagate. Defaults to 512 bytes, which is the 'classic' block size for hard drives since the early 1980s, but is not the most convenient. This will clone the entire drive, including the MBR (and therefore bootloader), all partitions, UUIDs, and data. # dd if=/dev/sda of=/dev/sdb bs=64K conv=noerror,sync status=progress Cloning an entire hard diskįrom physical disk /dev/sda to physical disk /dev/sdb: Note: Be careful that if the output partition of= ( sdb1 in the example) does not exist, dd will create a file with this name and will start filling up your root file system.

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