diff --git a/docs/external_usb_ssd_UAS.md b/docs/external_usb_ssd_UAS.md
index 2f27af6..d36cea1 100644
--- a/docs/external_usb_ssd_UAS.md
+++ b/docs/external_usb_ssd_UAS.md
@@ -6,3 +6,60 @@
 - **Main Controller:** ***ASM1153E***
 - **Support:** UASP Transfer Protocol
 
+#### OPEN Trim for external usb ssd
+
+```
+sudo fstrim -v /
+```
+
+**fstrim: /run/media/telgar/ssd: the discard operation is not supported**
+
+```
+$ lsblk --discard /dev/sda
+NAME   DISC-ALN DISC-GRAN DISC-MAX DISC-ZERO
+sdb           0        0B       0B         0
+├─sdba        0        0B       0B         0
+└─sdba        0        0B       0B         0
+```
+
+If the **DISC-MAX** value is **0B**, then TRIM is not **enabled**.
+
+Find the USB **idVendor** and **idProduct** :
+
+```
+$ lsusb
+...
+Bus 002 Device 002: ID 174c:1153 ASMedia Technology Inc. ASM1153 SATA 3Gb/s bridge
+...
+```
+
+Add **/etc/udev/rules.d/50-usb-ssd-trim.rules**
+
+```
+ACTION=="add|change", ATTRS{idVendor}=="174c", ATTRS{idProduct}=="1153", SUBSYSTEM=="scsi_disk", ATTR{provisioning_mode}="unmap"
+```
+
+Then reboot, the TRIM will be **enabled**.
+
+1st time, run "**fstrim -v /**" successfull:
+
+```
+$ sudo fstrim -v /
+/: 111.4 GiB (119574462464 bytes) trimmed
+```
+
+Automatic trimming
+
+The last thing you will need to do to make sure the TRIM command is run automatically in the background 
+
+(so you don't need to run fstrim manually) is to enable the built-in fstrim.timer.
+
+To do that, run the command:
+
+```
+$ sudo systemctl enable fstrim.timer
+```
+
+By default, it will run weekly. 
+
+All done.