Simulating Corruption

All,
First I simulated corruption and repair using a raid of two .img files in a
similar manner as here:
https://gist.github.com/MawKKe/caa2bbf7edcc072129d73b61ae7815fb

I am having issues doing the same on my actual disks and am curious if I
have configured something incorrectly. The disks are 4TB each and so I
started out by testing using 50GB partitions, otherwise cryptsetup takes
about 16 hours and then another 16 hours to assemble the raid. These are
the steps I took:

   - Create a 50G partition on each disk, /dev/sdb1 and /dev/sdd1
   - Encrypt each partition, cryptsetup -v --type luks2 --key-size 512
   --sector-size 4096 --integrity hmac-sha256 luksFormat /dev/sdXX
   /path/to/keyfile
   - Open devices, cryptsetup open --type luks cryptraidY /dev/sdXX
   --key-file /path/to/keyfile
   - Create raid, mdadm --create --verbose --level=10 --metadata=1.2
   --chunk=512 --raid-devices=2 --layout=f2 /dev/md/cryptraid
   /dev/mapper/cryptraid0 /dev/mapper/cryptraid1
   - Create filesystem, mkfs.xfs /dev/md/cryptraid
   - Scrub array, echo check > /sys/block/mdX/md/sync_action
   - dmesg shows, md: data-check of RAID array mdX / md: mdX data-check done
   - If I then try to corrupt a disk using dd, dd if=/dev/random
   of=/dev/sdd1 seek=1000 bs=1M count=1, then scrub, no errors are shown.


The only way I have been able to get the scrub to reveal errors if by doing
one of the following:

   - creating a file on the fs when mounted (seems like this should not),
   dd if=/dev/random of=~/Test/testfile bs=1M count=1
   - stop the raid, use dd on a partition as above (dd if=/dev/random
   of=/dev/sdd1 seek=1000 bs=1M count=1), assemble the raid, then scrub

Is this the expected behavior? Perhaps I am incorrectly using dd to
simulate corruption?

Thank you for any guidance.

Robby

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