#FreeBSD #zfs anybody know how to tell what the *actual* checksum chosen by OpenZFS is, on FreeBSD?
When a zpool is created by bsdinstall, it defaults to checksum=on, and a micro benchmark is done to choose the appropriate checksum (from fletcher4, sha256, sha512, skein, blake3).
I would like to know what that chosen checksum is.
https://openzfs.github.io/openzfs-docs/Basic%20Concepts/Checksums.html provides instructions for ZoL but its not matched on FreeBSD.
Sysctl shows only:
$ sysctl -a |egrep -i 'blake3|fletcher|sha2|sha5'
vfs.zfs.fletcher_4_impl: [fastest] scalar superscalar superscalar4 sse2 ssse3 avx2 avx512f avx512bw
vfs.zfs.sha512_impl: cycle [fastest] generic x64 avx avx2
vfs.zfs.sha256_impl: cycle [fastest] generic x64 ssse3 avx avx2 shani
vfs.zfs.blake3_impl: cycle [fastest] generic sse2 sse41 avx2 avx512
Which is not very helpful!
Inspecting zdb shows that the überblock uses fletcher4, if so that's a bad choice for almost all the machines I have, vs one of the more modern CPU-accelerated ones.
Uberblock:
magic = 0000000000bab10c
version = 5000
txg = 29818863
guid_sum = 12865431551488305392
timestamp = 1770722160 UTC = Tue Feb 10 11:16:00 2026
bp = DVA[0]=<0:1ef37817000:1000> DVA[1]=<0:1f26e5c1000:1000> DVA[2]=<0:8c341bf000:1000> [L0 DMU objset] fletcher4 uncompressed unencrypted LE contiguous unique triple size=1000L/1000P birth=29818863L/29818863P fill=75881 cksum=00000003035e0207:00000baf31d8f848:0016adf241101a15:1d6126f678dd7a91
