diff --git a/Documentation/ch-checksumming.rst b/Documentation/ch-checksumming.rst index 1554c580..5e47a6bf 100644 --- a/Documentation/ch-checksumming.rst +++ b/Documentation/ch-checksumming.rst @@ -1,32 +1,32 @@ -Data and metadata are checksummed by default, the checksum is calculated before -write and verified after reading the blocks from devices. The whole metadata -block has a checksum stored inline in the b-tree node header, each data block +Data and metadata are checksummed by default. The checksum is calculated before +writing and verified after reading the blocks from devices. The whole metadata +block has an inline checksum stored in the b-tree node header. Each data block has a detached checksum stored in the checksum tree. There are several checksum algorithms supported. The default and backward -compatible is *crc32c*. Since kernel 5.5 there are three more with different +compatible algorithm is *crc32c*. Since kernel 5.5 there are three more with different characteristics and trade-offs regarding speed and strength. The following list may help you to decide which one to select. -CRC32C (32bit digest) - default, best backward compatibility, very fast, modern CPUs have +CRC32C (32 bits digest) + Default, best backward compatibility. Very fast, modern CPUs have instruction-level support, not collision-resistant but still good error - detection capabilities + detection capabilities. -XXHASH (64bit digest) - can be used as CRC32C successor, very fast, optimized for modern CPUs utilizing - instruction pipelining, good collision resistance and error detection +XXHASH (64 bits digest) + Can be used as CRC32C successor. Very fast, optimized for modern CPUs utilizing + instruction pipelining, good collision resistance and error detection. -SHA256 (256bit digest) - a cryptographic-strength hash, relatively slow but with possible CPU - instruction acceleration or specialized hardware cards, FIPS certified and - in wide use +SHA256 (256 bits digest) + Cryptographic-strength hash. Relatively slow but with possible CPU + instruction acceleration or specialized hardware cards. FIPS certified and + in wide use. -BLAKE2b (256bit digest) - a cryptographic-strength hash, relatively fast with possible CPU acceleration - using SIMD extensions, not standardized but based on BLAKE which was a SHA3 - finalist, in wide use, the algorithm used is BLAKE2b-256 that's optimized for - 64bit platforms +BLAKE2b (256 bits digest) + Cryptographic-strength hash. Relatively fast, with possible CPU acceleration + using SIMD extensions. Not standardized but based on BLAKE which was a SHA3 + finalist, in wide use. The algorithm used is BLAKE2b-256 that's optimized for + 64-bit platforms. The *digest size* affects overall size of data block checksums stored in the filesystem. The metadata blocks have a fixed area up to 256 bits (32 bytes), so @@ -61,8 +61,8 @@ The accelerated versions are however provided by the modules and must be loaded explicitly (:command:`modprobe sha256`) before mounting the filesystem to make use of them. You can check in :file:`/sys/fs/btrfs/FSID/checksum` which one is used. If you see *sha256-generic*, then you may want to unmount and mount the filesystem -again, changing that on a mounted filesystem is not possible. -Check the file :file:`/proc/crypto`, when the implementation is built-in, you'd find +again. Changing that on a mounted filesystem is not possible. +Check the file :file:`/proc/crypto`, when the implementation is built-in, you'd find: .. code-block:: none @@ -72,7 +72,7 @@ Check the file :file:`/proc/crypto`, when the implementation is built-in, you'd priority : 100 ... -while accelerated implementation is e.g. +While accelerated implementation is e.g.: .. code-block:: none