FileDescriptor getFileDescriptorFromFileChannel(FileChannel fileChannel) throws Exception {
    Field field = FileChannelImpl.class.getDeclaredField("fd");
    field.setAccessible(true);
    return (FileDescriptor) field.get(fileChannel);
  }
Test {@link BlobStore#testStorageAvailability()}. Create a blob store with the existing log segment files, it should
return true from the method. After deleting the log segment files and invalidate the page cache for log segment files,
it should return false.
@throws Exception
ambry-store/src/test/java/com/github/ambry/store/BlobStoreTest.java