bugfix/CSTACKEX-131: ISCSI VM created with small sized template which takes less than 30s copy will be a dummy VM (#42)

### Description

This PR...
<!--- Describe your changes in DETAIL - And how has behaviour
functionally changed. -->

<!-- For new features, provide link to FS, dev ML discussion etc. -->
<!-- In case of bug fix, the expected and actual behaviours, steps to
reproduce. -->

<!-- When "Fixes: #<id>" is specified, the issue/PR will automatically
be closed when this PR gets merged -->
<!-- For addressing multiple issues/PRs, use multiple "Fixes: #<id>" -->
<!-- Fixes: # -->

<!---
*******************************************************************************
-->
<!--- NOTE: AUTOMATION USES THE DESCRIPTIONS TO SET LABELS AND PRODUCE
DOCUMENTATION. -->
<!--- PLEASE PUT AN 'X' in only **ONE** box -->
<!---
*******************************************************************************
-->

### Types of changes

- [ ] Breaking change (fix or feature that would cause existing
functionality to change)
- [ ] New feature (non-breaking change which adds functionality)
- [x] Bug fix (non-breaking change which fixes an issue)
- [ ] Enhancement (improves an existing feature and functionality)
- [ ] Cleanup (Code refactoring and cleanup, that may add test cases)
- [ ] Build/CI
- [ ] Test (unit or integration test code)

### Feature/Enhancement Scale or Bug Severity

#### Feature/Enhancement Scale

- [ ] Major
- [ ] Minor

#### Bug Severity

- [ ] BLOCKER
- [ ] Critical
- [ ] Major
- [ ] Minor
- [ ] Trivial

### Screenshots (if appropriate):
<img width="1451" height="117" alt="image"
src="https://github.com/user-attachments/assets/3af9c3b4-e834-42f9-925d-6e87028fe3bf"
/>
<img width="1491" height="574" alt="image"
src="https://github.com/user-attachments/assets/ac2a39c2-d32f-4c22-89d1-261a2e15bdd7"
/>


### How Has This Been Tested?

<!-- Please describe in detail how you tested your changes. -->
<!-- Include details of your testing environment, and the tests you ran
to -->

#### How did you try to break this feature and the system with this
change?

<!-- see how your change affects other areas of the code, etc. -->

<!-- Please read the
[CONTRIBUTING](https://github.com/apache/cloudstack/blob/main/CONTRIBUTING.md)
document -->

---------

Co-authored-by: Srivastava, Piyush <Piyush.Srivastava@netapp.com>

Author: piyush5netapp

plugins/hypervisors/kvm/src/main/java/com/cloud/hypervisor/kvm/storage/IscsiAdmStorageAdaptor.java

@@ -510,6 +510,19 @@ public KVMPhysicalDisk copyPhysicalDisk(KVMPhysicalDisk srcDisk, String destVolu
         try {
             QemuImg q = new QemuImg(timeout);
             q.convert(srcFile, destFile);
+            // Below fix is required when vendor depends on host based copy rather than storage CAN_CREATE_VOLUME_FROM_VOLUME capability
+            // When host based template copy is triggered , small size template sits in RAM(depending on host memory and RAM) and copy is marked successful and by the time flush to storage is triggered
+            // disconnectPhysicalDisk would disconnect the lun , hence template staying in RAM is not copied to storage lun. Below does flushing of data to storage and marking
+            // copy as successful once flush is complete.
+            Script flushCmd = new Script(true, "blockdev", 0, logger);
+            flushCmd.add("--flushbufs", destDisk.getPath());
+            String flushResult = flushCmd.execute();
+            if (flushResult != null) {
+                logger.warn("iSCSI copyPhysicalDisk: blockdev --flushbufs returned: {}", flushResult);
+            }
+            Script syncCmd = new Script(true, "sync", 0, logger);
+            syncCmd.execute();
+            logger.info("iSCSI copyPhysicalDisk: flush/sync completed ");
         } catch (QemuImgException | LibvirtException ex) {
             String msg = "Failed to copy data from " + srcDisk.getPath() + " to " +
                     destDisk.getPath() + ". The error was the following: " + ex.getMessage();