Clarify custom installation requirements for custom storage paths (DOC-635)

- Update install-on-linux.md to clearly explain when custom installation is needed
- Add specific guidance about custom storage path requirements
- Enhance customize-install-directories.md with troubleshooting section
- Include specific error message and resolution steps
- Add cross-references between installation and storage documentation
- Address fragmented user experience by connecting related concepts

Resolves DOC-635

Author: mich-elle-luna

content/operate/rs/installing-upgrading/install/customize-install-directories.md

@@ -14,6 +14,10 @@ When you install Redis Enterprise Software on Red Hat Enterprise Linux, you can
 
 The files are installed in the `redislabs` directory located in the path that you specify.
 
+{{< note >}}
+Custom installation is required if you plan to specify custom storage paths for persistent or ephemeral storage during cluster setup. If you install Redis Enterprise Software to default directories, you cannot specify custom storage paths during cluster creation.
+{{< /note >}}
+
 ## Considerations
 
 - When you install with custom directories, the installation does not run as an RPM file.
@@ -76,6 +80,45 @@ To configure different mount points for data and log directories, use symbolic l
     ln -s /var/opt/redislabs/log </path/to/log/mount/point>
     ```
 
+## Custom storage paths
+
+When you install Redis Enterprise Software to custom directories, you can specify custom storage paths for persistent and ephemeral storage during [cluster setup]({{< relref "/operate/rs/clusters/new-cluster-setup" >}}) or when [adding nodes]({{< relref "/operate/rs/clusters/add-node" >}}).
+
+### Prerequisites for custom storage paths
+
+Before specifying custom storage paths during cluster setup:
+
+1. Install Redis Enterprise Software to custom directories using the `--install-dir`, `--config-dir`, and `--var-dir` flags.
+
+2. Ensure proper permissions: The custom storage directories must have full permissions for the `redislabs` user and group (`redislabs:redislabs`).
+
+3. Verify mount points: Custom storage paths must be properly mounted and accessible.
+
+### Troubleshooting custom storage paths
+
+If you encounter the error "path entered is not mounted. Please correct" when specifying custom storage paths:
+
+1. Verify the installation method: Ensure Redis Enterprise Software was installed using custom directories. If you used the default installation (`sudo ./install.sh` without custom directory flags), you cannot specify custom storage paths.
+
+2. Check directory permissions: Ensure the `redislabs` user has full access to the specified directories:
+   ```sh
+   sudo chown -R redislabs:redislabs /path/to/custom/storage
+   sudo chmod -R 755 /path/to/custom/storage
+   ```
+
+3. Verify mount points: Confirm the storage path is properly mounted:
+   ```sh
+   df -h /path/to/custom/storage
+   mount | grep /path/to/custom/storage
+   ```
+
+4. Check directory existence: Ensure the directory exists and is accessible:
+   ```sh
+   ls -la /path/to/custom/storage
+   ```
+
+For more information about storage requirements, see [Persistent and ephemeral node storage]({{< relref "/operate/rs/installing-upgrading/install/plan-deployment/persistent-ephemeral-storage" >}}).
+
 ## Limitations
 
 Several Redis Enterprise Software installation reference files are installed to the directory `/etc/opt/redislabs/` even if you use custom installation directories.

content/operate/rs/installing-upgrading/install/install-on-linux.md

@@ -29,37 +29,57 @@ To install Redis Enterprise Software, use the command line:
 1.  _(Optional)_ Use the {{< download "GPG key file" "../GPG-KEY-redislabs-packages.gpg" >}} to confirm the authenticity of Ubuntu/Debian or RHEL RPM packages:
 
     - For Ubuntu:
-        1. Import the key:  
+        1. Import the key:
         ```sh
         gpg --import <path to GPG key>
-        ```  
-        2. Verify the package signature: 
-        ```sh 
+        ```
+        2. Verify the package signature:
+        ```sh
         dpkg-sig --verify </path-to/package.deb>
         ```
 
     - For RHEL:
-        1. Import the key:  
+        1. Import the key:
         ```sh
         rpm --import <path to GPG key>
         ```
-        2. Verify the package signature:  
+        2. Verify the package signature:
          ```sh
          rpm --checksig </path-to/package.rpm>
          ```
 
-1. To start the installation process, run the installation script. See [installation script options]({{< relref "/operate/rs/installing-upgrading/install/install-script" >}}) for a list of command-line options you can add to the following command:
+1. To start the installation process, run the installation script:
 
+    **For standard installation:**
     ```sh
     sudo ./install.sh
     ```
 
+    **For custom installation directories:**
+
+    If you need to specify custom storage paths for persistent or ephemeral storage during cluster setup, you must install Redis Enterprise Software to custom directories. See [installation script options]({{< relref "/operate/rs/installing-upgrading/install/install-script" >}}) for a complete list of command-line options.
+
+    ```sh
+    sudo ./install.sh --install-dir <path> --config-dir <path> --var-dir <path>
+    ```
+
+    For detailed information about custom installations, see [Customize installation directories]({{< relref "/operate/rs/installing-upgrading/install/customize-install-directories" >}}).
+
     {{< note >}}
-- The Redis Enterprise Software files are installed in the default [file locations]({{< relref "/operate/rs/installing-upgrading/install/plan-deployment/file-locations.md" >}}). 
+- The Redis Enterprise Software files are installed in the default [file locations]({{< relref "/operate/rs/installing-upgrading/install/plan-deployment/file-locations.md" >}}) unless you specify custom directories.
 - By default, Redis Enterprise Software runs on the OS as the `redislabs` user and `redislabs` group. If needed, you can [specify a different user and group]({{< relref "/operate/rs/installing-upgrading/install/customize-user-and-group.md" >}}) during the installation.
 - You must either be the root user or use `sudo` to run the installation script.
     {{< /note >}}
 
+    ### When to use custom installation directories
+
+    You should use custom installation directories if you need to:
+
+    - Specify custom storage paths for persistent or ephemeral storage during cluster setup
+    - Install Redis Enterprise Software in non-default locations for organizational or security requirements
+    - Avoid using root directories for the installation
+    - Meet specific compliance or infrastructure requirements
+
 1. Answer the [installation questions]({{< relref "/operate/rs/installing-upgrading/install/manage-installation-questions.md" >}}) when shown to complete the installation process.
 
     {{< note >}}

content/operate/rs/installing-upgrading/install/plan-deployment/file-locations.md

@@ -41,3 +41,7 @@ You can change these file locations for:
 
 - [Ephemeral and persistence storage]({{< relref "/operate/rs/clusters/new-cluster-setup.md" >}}) during cluster setup
 - [Socket files]({{< relref "/operate/rs/installing-upgrading/configuring/change-location-socket-files.md" >}}) after cluster setup
+
+{{< note >}}
+To specify custom storage paths for ephemeral and persistent storage during cluster setup, you must install Redis Enterprise Software using [custom installation directories]({{< relref "/operate/rs/installing-upgrading/install/customize-install-directories" >}}). If you use the default installation, you cannot specify custom storage paths and will receive a "path not mounted" error.
+{{< /note >}}