Keep the CTP7 in read-only mode except during maintenance

The title says it all... This MR adds a few instructions on keeping the CTP7 persistent volume in read-only mode during data taking to prevent data corruption in case of a sudden power cut.

Fixes #2 (closed).

docs/expert/p5-operations/installation-maintenance.md

@@ -12,6 +12,20 @@ Failing to follow the instructions or failing to react to unexpected events can
     * System modifications to the GEM machines can (but should not) be carried on by members of the `gemsudoers` group.
     * Traditionally, the `gempro` and `gemsudoers` groups are kept in sync' and meant for DAQ experts; the `cms_gem_librarian` is a sub-group meant for administrators and superusers.
 
+!!! warning
+    All CTP7 volumes are kept in read-only mode during normal operations in order to avoid data corruption in case of a sudden power cut.
+    During backend boards maintenance, the `/mnt/persistent` partition must be remounted in read-write mode:
+    ``` sh
+    # from gempro@gemvm-control
+    mussh -m 13 -H /gemdata/config/ctp7-ge* -l root -c 'mount -o remount,rw /mnt/persistent'
+    ```
+    Do no forget to put back the partition in read-only mode after maintenance:
+    ``` sh
+    # from gempro@gemvm-control
+    mussh -m 13 -H /gemdata/config/ctp7-ge* -l root -c 'mount -o remount,ro /mnt/persistent'
+    ```
+    Such an operation is taken care of automatically in the `push-configuration.sh` script & co.
+
 ## Online software
 
 ### Client software