Ubuntu – NVMe SSD is not detected by the Ubuntu 20.04 installer

Well after a lot of google search I came across this post. The issue was at the BIOS level. In case of Dell desktops and laptops - one has to set the SATA mode to AHCI rather than the default Raid On. If you don't follow the above post - your machine won't boot Windows 10 as the AHCI driver is by default not installed. That's why one need to go into the safemode first then make the changes in BIOS and then disable the safemode. Being in the safemode - it installs the AHCI drivers via which O/S can talk to the drives. After this I booted via the live USB and i can see the Samsung PCIe NVME SSD being visible from the gparted.

I believe it is enabled by default. You can check it:

cat /sys/block/nvme0n1/queue/write_cache
write back

Probably this is optimal setting

Write through caching:
When the controller receives a write request from the host, it stores the data in its cache module, writes the data to the disk drives, then notifies the host when the write operation is complete. This process is calles write-trough caching because the data actually passes through-and is stored in- the cache memory on its way to the disk drives.

Write back caching:
This caching technique improves the subsystem's response time to write requests by allowing the controller to declare the write operation 'complete' as soon as the data reaches its cache memory. The controller performs the slower operation of writing the data to the disk drives at a later time.

In most cases nvme ssds has built in ddr cache like 500MB or 1GB (probably managed by disk firmware if not let's someone correct me because maybe that's the problem)

You can check if trim is working as expected by manually executing sudo fstrim -av and test write speed in real life by copying and pasting big file and measure time taken.

But there are still slow writes and it seems like these are handling in this way by kernel itself (maybe some reliability syncing):
SSD slow write speed on Ubuntu