Update 2.balance-syntax.md (#1037)

docs-2.0/3.ngql-guide/18.operation-and-maintenance-statements/2.balance-syntax.md

@@ -10,8 +10,12 @@ The `BALANCE` statements are listed as follows.
 
 |Syntax|Description|
 |:---|:---|
-|`BALANCE IN ZONE [REMOVE <ip>:<port> [,<ip>:<port> ...]]`| Starts a job to balance the distribution of storage partitions in each zone in the current graph space. It returns the job ID. You can use the `REMOVE` option to specify the Storage services that you want to clear for easy maintenance.|
-|`BALANCE ACROSS ZONE [REMOVE "zone_name" [,"zone_name" ...]]`| Starts a job to balance the distribution of storage partitions across each zone in the current graph space. It returns the job ID. You can use the `REMOVE` option to specify the zones that you want to clear for easy maintenance.|
+|`BALANCE IN ZONE [REMOVE <ip>:<port> [,<ip>:<port> ...]]`| Starts a job to balance the distribution of storage partitions in each zone in the current graph space. It returns the job ID. You can use the `REMOVE` option to specify the Storage services that you want to clear. The partitions of these services will be moved to other services for easy maintenance.|
+|`BALANCE ACROSS ZONE [REMOVE "zone_name" [,"zone_name" ...]]`| Starts a job to balance the distribution of storage partitions across each zone in the current graph space. It returns the job ID. You can use the `REMOVE` option to specify the zones that you want to clear. The partitions of these services will be moved to other services for easy maintenance.|
 |`BALANCE LEADER`| Starts a job to balance the distribution of storage leaders across each zone in the current graph space. It returns the job ID.|
 
+!!! note
+
+    `REMOVE` can only clear the partitions of the current graph space. If a Storage service has a large number of graph spaces, you need to switch to all different graph spaces to perform the `REMOVE` operation.
+
 For details about how to view, stop, and restart a job, see [Job manager and the JOB statements](4.job-statements.md)。