marko10_000
/
btrfs-progs
forked from Mirrors/btrfs-progs
1
0
Fork 0
Code Issues Pull Requests Releases Wiki Activity

btrfs-progs: docs: checksum algorithms 

Signed-off-by: David Sterba <dsterba@suse.com>
master
David Sterba 2019-11-05 21:26:14 +01:00
parent c981414ea3
commit a517225ece
1 changed files with 49 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

51
Documentation/btrfs-man5.asciidoc
View File

@ -12,6 +12,7 @@ tools. Currently covers:
. mount options
. filesystem features
. checksum algorithms
. filesystem limits
. bootloader support
. file attributes
@ -532,8 +533,8 @@ explicitly asked for so accidental use will not create incompatibilities.
There are several classes and the respective tools to manage the features:
at mkfs time only::
This is namely for core structures, like the b-tree nodesize, see
`mkfs.btrfs`(8) for more details.
This is namely for core structures, like the b-tree nodesize or checksum
algorithm, see `mkfs.btrfs`(8) for more details.
after mkfs, on an unmounted filesystem::
Features that may optimize internal structures or add new structures to support
@ -671,6 +672,52 @@ temporarily activated. The operation must finish first.
--------------------
CHECKSUM ALGORITHMS
-------------------
There are several checksum algorithms supported. The default and backward
compatible 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
instruction-level support, not collision-resistant but still good error
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
*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
*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
The 'digest size' affects overall size of data block checksums stored in the
filesystem. The metadata blocks have a fixed area up to 256bits (32 bytes), so
there's no increase. Each data block has a separate checksum stored, with
additional overhead of the b-tree leaves.
Approximate relative performance of the algorithms, measured against CRC32C
using reference software implementations on a 3.5GHz intel CPU:
[ cols="^,>,>",width="50%" ]
|================================
h| Digest h| Cycles/4KiB h| Ratio
| CRC32C | 1700 | 1.00
| XXHASH | 2500 | 1.44
| SHA256 | 105000 | 61
| BLAKE2b | 22000 | 13
|================================
FILESYSTEM LIMITS
-----------------