add encrypted btrfs on ssd nvme tips

README.md

@@ -126,3 +126,58 @@ Make the changes to `/usr` persist reboots
 ```bash
 rpm-ostree usroverlay --hotfix
 ```
+
+## encrypted BTRFS on ssd-like disk maintenance/health
+
+It is **very** important for performance to have trimming working. To test it
+run the below to trim all mounted filesystems (can take long time, like over
+10,20 minutes) (if root disk is not trimmed, it have discard not enabled at
+some level):
+
+```bash
+fstrim -av
+```
+
+If trimming is not working, check the below:
+
+- `/etc/crypttab` if it have discard set for root
+- `discard=async`, `discard=sync`, or `discard` flags set in `/etc/fstab`
+- `lsblk -o +DISC-GRAN,DISC-MAX` - the additional columns should have non-zero values
+- `cryptsetup luksDump /dev/nvme0n1p3` - if flag `allow-discards` is set
+(optional but best way to make cryptsetup allow discards by default)
+
+Setting performance improving flags on luks volume:
+
+```bash
+cryptsetup refresh \
+    --allow-discards \
+    --perf-no_read_workqueue \
+    --perf-no_write_workqueue \
+        --persistent \
+            /dev/mapper/<disk>
+```
+
+Arch wiki about workqueues: https://wiki.archlinux.org/title/Dm-crypt/Specialties#Disable_workqueue_for_increased_solid_state_drive_(SSD)_performance
+
+Recommended flags for btrfs volume mounting (compression flag optional, I guess):
+
+```
+noatime,space_cache=v2,discard=async,compress-force=zstd:1
+```
+
+If for some reason `space_cache` is not set properly on volume mount, do this
+, (fs need to be unmounted):
+
+- clear any v1 and v2 space_cache
+- mount with space_cache=v2 flag
+- check if flag is set correctly (maybe also create some file there?)
+
+```bash
+btrfs check --clear-space-cache v1 /dev/mapper/<device>
+btrfs check --clear-space-cache v2 /dev/mapper/<device>
+
+mount -o space_cache=v2 /dev/mapper/<device> /mnt
+mount | grep space_cache
+echo "hello" > /mnt/some/path/file.txt
+umount /mnt
+```