Add Bell decommission banner.

Author: Guangzhen-Jin

docs/index.md

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-<!-- !!! Warning "Announcement"
-    **This is a demo site.** You are visiting a demo site designed for testing purposes only. Contents on this website may not reflect production RCAC resources. Check [rcac.purdue.edu](https://www.rcac.purdue.edu) for official information. -->
+??? info "Important: RCAC to decommission Bell on October 31, 2026"
+    **The Bell Community cluster has reached the end of its life, and we are taking steps to decommission this cluster on October 31, 2026.** 
+    
+    Since its introduction in 2020, Bell has provided a cost-effective platform for a diverse spectrum of science and engineering workloads. Bell’s decommissioning is a crucial step towards creating capacity for novel systems that meet emerging research needs.  
+    
+    We recommend that you start backing up your data to appropriate storage systems such as [Data Depot](https://docs.rcac.purdue.edu/userguides/depot/) and [Fortress](https://docs.rcac.purdue.edu/userguides/fortress/). You can use [Globus](https://docs.rcac.purdue.edu/userguides/bell/storage/globus/) or other tools for your data transfer needs. 
+    
+    **After 5:00 PM on Friday, October 30, 2026, RCAC STAFF WILL NOT be able to retrieve any data left in the Bell scratch filesystem.** 
+    
+    To support research groups planning work beyond Bell’s retirement, RCAC recommends [Gautschi compute cluster](https://www.rcac.purdue.edu/compute/gautschi) as the successor community cluster. Gautschi compute cluster has considerable advantages over Bell in many respects. It offers significantly more processing cores per node, performant GPUs available via standby scheduling, and an interconnect designed for current high-performance and AI-enabled workloads. 
+    
+    Please also feel free to contact us at [rcac-help@purdue.edu](mailto:rcac-help@purdue.edu) if you have any questions or need support and visit [our post at RCAC website](https://www.rcac.purdue.edu/news/7776) for additional details.
 
 ??? info "Important: Use Microsoft Authenticator to Access Purdue RCAC Resources Starting May 11, 2026"
     **Beginning May 11, 2026, RCAC will move from Duo Mobile to Microsoft Authenticator for logging in to Purdue’s research computing and supercomputing systems (excluding Anvil).**