docs: Update description on size_gb in disk field

Google APIs · copybara-github · commit a5482b455263 · 2023-08-29T17:20:26.000-07:00
PiperOrigin-RevId: 561181917
diff --git a/google/cloud/batch/v1/job.proto b/google/cloud/batch/v1/job.proto
@@ -283,14 +283,23 @@ message AllocationPolicy {
 
     // Disk size in GB.
     //
-    // For persistent disk, this field is ignored if `data_source` is `image` or
-    // `snapshot`.
-    // For local SSD, size_gb should be a multiple of 375GB,
-    // otherwise, the final size will be the next greater multiple of 375 GB.
-    // For boot disk, Batch will calculate the boot disk size based on source
+    // **Non-Boot Disk**:
+    // If the `type` specifies a persistent disk, this field
+    // is ignored if `data_source` is set as `image` or `snapshot`.
+    // If the `type` specifies a local SSD, this field should be a multiple of
+    // 375 GB, otherwise, the final size will be the next greater multiple of
+    // 375 GB.
+    //
+    // **Boot Disk**:
+    // Batch will calculate the boot disk size based on source
     // image and task requirements if you do not speicify the size.
-    // If both this field and the boot_disk_mib field in task spec's
-    // compute_resource are defined, Batch will only honor this field.
+    // If both this field and the `boot_disk_mib` field in task spec's
+    // `compute_resource` are defined, Batch will only honor this field.
+    // Also, this field should be no smaller than the source disk's
+    // size when the `data_source` is set as `snapshot` or `image`.
+    // For example, if you set an image as the `data_source` field and the
+    // image's default disk size 30 GB, you can only use this field to make the
+    // disk larger or equal to 30 GB.
     int64 size_gb = 2;
 
     // Local SSDs are available through both "SCSI" and "NVMe" interfaces.
