User:Filam/Block size
The dd command copies and converts raw data at a low level. The block size option (i.e. bs=
) defines the number of bytes involved in a single read or write operation. There is a great deal of confusion about the optimal value for this option.[1]
- Unix device files use 512-byte blocks as their allocation unit by default.
If you have a Advanced Format hard drive it is recommended that you specify a block size larger than the default 512 bytes. To speed up the overwriting process choose a block size matching your drive's physical geometry by appending the block size option to the dd command (i.e. bs=4096
).
The block size value may be followed by the following multiplicative suffixes: c
=1, w
=2, b
=512, kB
=1000, K
=1024, MB
=10002, M
=10242, etc.
Print block size
To print the block size of the device issue the following command:
# dumpe2fs -h /dev/sdX | grep 'Block size:'
For more information read How to Find the Block Size on The Linux Information Project and the Block size section in the core GNU utilites manual.
Disparate examples
This section lists examples of the dd block size flag (i.e. bs=
) on English language pages. The following examples all come from the first page of a search for "bs=".
dd if=/dev/zero of=rootfs bs=1MB count=1000
# dd if=/dev/zero of=/swapfile bs=1024 count=512288
# dd count=1 bs=512 if=/dev/zero of=/dev/sdx
dd if=$my_boot_part of=/media/win/linux.bin bs=512 count=1
# dd if=/dev/urandom of=mykeyfile bs=512 count=4
# dd if=/dev/urandom of=secretkey bs=512 count=4
$ dd if=/dev/zero of=image.img bs=1G count=0 seek=[NUMBER_OF_GB]
dd bs=4k if=/dev/hdc1 of=/dev/hdj1