Update volume-migration.md

docs/architecture/concepts/volume-migration.md

@@ -3,12 +3,21 @@ title: "Volume Migration"
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-Volume migration in simplyblock enables the online relocation of logical volumes between storage nodes without service
-interruption. This is essential for planned maintenance, hardware replacement, capacity rebalancing, and infrastructure
-modernization.
+Simplyblock distributes storage across two layers. The front storage, which acts as "docking point" for clients connecting 
+to volumes remotely via NVMe-oF (TCP, RoCEv2), and the back storage, which serves the actual cluster storage capacity. 
+The front storage accesses back storage both locally and remotely. Remote access itself uses NVMe-oF.
 
-As simplyblock back storage is entirely distributed, volume migration does not require actual data movement! In fact, only
-meta-data and extent headers are updated. 
+Volume migration in simplyblock enables the online relocation of logical volumes (front storage or "docking points") 
+between storage nodes without service interruption and almost instantly. This is possible, because front storage has
+remote access to all devices in the cluster and thus exists essentially "in memory" only. 
+
+Volume migrations are performed automatically based on operator decisions to either pre-serve data locality of workloads or 
+to to balance I/O performance across cluster nodes. This is required since the front storage does the "heavy-lifting" in I/O processing
+and runs all the data services. Additionally, volume migration is is used to drain nodes in case they need to be removed from the cluster
+(hardware replacement, infrastructure modernization).
+
+While most of the volume migrations happen "under the hood", users can also explicitely initiate migrations (e.g., to 
+move particular, I/O-heavy volumes to particular nodes).
 
 ## How Volume Migration Works