We can monitor the backup operation to check the current status using the following call:

http://localhost:8983/solr/myschema/replication?command=details&wt=xml

The output will be something like this: 

<lst name="backup">
    <str name="startTime">Tue Jan 30 14:32:12 DAVT 2018</str>
    <int name="fileCount">15</int>
    <str name="status">success</str>
    <str name="snapshotCompletedAt">Tue Jan 30 14:32:12 DAVT 2018</str>
    <str name="snapshotName">demobackup</str>
</lst>

If there is a failure, then we will get snapShootException in the response.