abh1sar commented on code in PR #14194:
URL: https://github.com/apache/cloudstack/pull/14194#discussion_r4250573117


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agent/src/main/java/com/cloud/agent/properties/AgentProperties.java:
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@@ -636,6 +636,23 @@ public class AgentProperties{
      */
     public static final Property<String> KVM_SCRIPTS_DIR = new 
Property<>("kvm.scripts.dir", "scripts/vm/hypervisor/kvm");
 
+    /**
+     * Host-local parent directory for the NAS backup pull-mode scratch area: 
the NBD socket and
+     * the libvirt-managed fleecing (copy-before-write) images used while 
backing up a running VM
+     * on raw block-device storage such as LINSTOR/DRBD.
+     * <p>
+     * Must be on a real on-disk filesystem with room for the guest's write 
churn during a backup,
+     * and must NOT be on the NAS share: copy-before-write runs inline with 
guest writes, so a slow
+     * or remote location stalls the VM. Keep the path short — the resulting 
socket path is subject
+     * to the kernel's 108-byte UNIX socket limit.
+     * <p>
+     * Data type: String.<br>
+     * Default value: <code>/var/tmp</code>
+     *
+     * @since 4.22.0
+     */
+    public static final Property<String> NAS_BACKUP_PULL_SCRATCH_DIR = new 
Property<>("nas.backup.pull.scratch.dir", "/var/tmp");

Review Comment:
   If the scratch dir gets full, the VM writes are stalled and it is paused. If 
I am not wrong, the VM is never resumed.
   Consider either creating the scratch dir as a new volume on the Linstor pool 
itself / do a space check before starting backup / test the pause and resume 
workflow.



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