How to diplomatically phrase an "out of scope" to customer email. Wow. Not 100% grammatically correct but very diplomatic.

Thanks for sharing with us on the details and it's good to know the issue has been fixed.

Although we deliver a project based on best practice and experiences from past projects, but every project has different situations, hereby we implement user pilot stage to discover and fix potential issues, during the pilot stage of our project, we worked with your team covered as many scenarios as possible,  that is very important for the sanity of the deployment and I believe there haven’t been too much outstanding issues in past months. However,  to be very frankly, the concurrency of external user wasn’t included,  from a methodology point of view, such hidden issues normally will be further discovered and fixed during the gradually production rolling out, either my team or technical support team will help on this along the way.

Thanks for the understanding and have a nice day!

How to reduce (Tweak) Synology Rebuild time - Use at your own risk!

echo 90 > /proc/sys/vm/dirty_ratio
echo 80 > /proc/sys/vm/dirty_background_ratio
echo 6000 > /proc/sys/vm/dirty_expire_centisecs
echo 4000 > /proc/sys/vm/dirty_writeback_centisecs

For the next two, change "sda" to the device name; you may need to repeat for each device.
echo deadline > /sys/block/sda/queue/scheduler
echo 16384 > /sys/block/sda/queue/nr_requests

For the next two, change "md2" to the volume name if different; you may need to repeat for each volume.
echo 524288 > /sys/block/md2/md/stripe_cache_size
blockdev --setra 4096 /dev/md2

The following line can only be enabled while the array is healthy
mdadm --grow /dev/md2 --bitmap=internal

Edit /etc/sysctl.conf to add this line
dev.raid.speed_limit_min=100000