Hi linux-btrfs,
Step to reproduce
1) mkfs.btrfs -draid6 -mraid6 /dev/sd[abcdefgh]
2) mount
-onoatime,nodiratime,thread_pool=24,max_inline=0,ssd_spread,compress-force=zstd
/dev/sda /mnt/test/
3) btrfs subvol create /mnt/test/subvol/
4) dd if=/dev/zero of=/mnt/test/subvol/test.dat bs=1M count=65536
5) btrfs subvol snapshot -r /mnt/test/subvol /mnt/test/subvol.ro
6) btrfs send /mnt/test/subvol.ro | pv >/dev/null
64,1GiB 0:01:18 [ 833MiB/s] - fast
7) for i in {1..16384}; do echo $i; printf '\x01\x02\x03' | dd
of=/mnt/test/subvol/test.dat bs=1 seek=$(($i * 1024 * 1024)) count=3
conv=notrunc; done
8) btrfs send /mnt/test/subvol.ro | pv >/dev/null
I stop it at 0:01:18
464MiB 0:01:18 [4,67MiB/s] - very very slow
uname -a
Linux storage.domain.com 5.3.7-200.fc30.x86_64 #1 SMP Fri Oct 18
20:13:59 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux
