1/27/2024 0 Comments Dd linux copy fast transfer# dd if=/dev/sda conv=sync,noerror bs=64K | gzip -c > /path/to/ Then mount the external hard drive and backup the drive: 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.If you are cloning a GPT disk, you can use sgdisk to randomize the disk and partition GUIDs and regain their uniqueness.For swap partitions, use mkswap -U random /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.
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