Instant Scan Frequently Asked Questions
  • 13 Nov 2023
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Instant Scan Frequently Asked Questions

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  • PDF

Article Summary


Retrospect 10 for Macintosh and Retrospect 8 for Windows introduced a new feature called Instant Scan. This feature allows each computer on your network to pre-scan a volume so that the backup of that computer can take place without a long scan of the entire volume.

Mac Customers: Please note that Instant Scan is not supported with APFS.

# How does Instant Scan work?

Instant Scan runs as a background process on Retrospect servers and clients to maintain a list of all the files and folders present on HFS+ (Mac) and NTFS (Windows) volumes. It uses FSEvents on OS X and the USN change journal on Windows to keep track of new, changed, moved, and deleted files. When it’s time for a backup or a restore, Retrospect gets the file listing from Instant Scan, instead of needing to scan each volume, as it did in previous versions. For a volume with a million files, this can easily save 10 minutes per backup.

Why does RetroISA use up such a high CPU load?

The RetroISA process must perform a scan on your system after it has been installed. This scan can take from 15 to 60 minutes depending on how many files you have. Once the scan is done, the CPU load should drop to under 1% in most cases. You will sometimes see the RetroISA process jump for short periods of time while the scan files are updated.

How can I tell if Retrospect is using Instant Scan for a specific volume?

During a traditional scan, Retrospect will count each file and folder on a disk. You will not see that long count with Instant Scan. Your operations log will contain an entry that looks similar to this for each volume it backs up:    + Executing Immediate Backup at 10/30/2012 7:32 AM (Execution unit 1) To Backup Set Backup Set A…​   - 10/30/2012 7:32:13 AM: Copying Local Disk (C:) Using Instant Scan

What types of volumes does this feature support?

Locally mounted NTFS volumes when using Retrospect for Windows.  

Disks locally mounted to the desktop of your Macintosh and Windows computers using the Retrospect Client software.

Mac OS Extended volumes mounted to the desktop of your Macintosh backup computer and clients.

It does not work with NAS devices or Linux clients.

How is the volume scan data tracked?

Each disk that is scanned by Retrospect is tracked by a "scan file" located in the following paths

  • Windows XP/2003: C:\Documents and Settings\All Users\Application Data\RetroISA\RetroISAScans
  • Windows Vista and later: C:\Program Data\RetroISA\RetroISAScans
  • Macintosh: /Library/Application Support/Retrospect/RetroISAScans

If I think the scan file is corrupted, can rebuild the scan file?

Instant Scan files can be corrupted if the scan is aborted during a power loss or crash scenario. In these cases, the Instant Scan process will automatically delete these files on relaunch.

How can I identify the RetroISA process?

On the Macintosh you can see the RetroISA process inside your OS X Activity Monitor. On Windows, you will see a RetroISA process inside the task manager and within the Services control panel.

I keep seeing the RetroISA process fluctuate how much CPU it uses during the day, even if no backup is running. Is this normal?

Yes, this is totally normal. RetroISA will run scan updates during the day so that your backup will contain the most current data possible.

If I change a file on my disk and immediately run a backup or trigger a Backup on Demand, will that file be included in my backup?

It is possible that a newly saved file will not be included in a backup that runs within 30 minutes of a file change. If you were to copy a large number of files to a volume, that will result in a longer amount of time to scan and update the RetroISA scan files. The RetroISA process must have time to scan and update the Scan File before a backup for those file changes to be seen when the backup starts. A scan file may be updated in as little as 5 minutes after a file has changed, but on larger volumes it could take longer to update the scan files. You may also see error -1101 (File/Folder not found) if a file was deleted from your disk between the last time a scan file was updated and when you have attempted a backup of a disk.

While backups that are triggered immediately after a file is saved may not see that file, the lag time is only five to ten minutes for file changes to be "seen" by Instant Scan.

With this new Instant Scan feature, can I back up more computers every night?

Your time savings will happen during the volume scan at the beginning of a backup. If the traditional scanning of your disk takes about 10 minutes, then the Instant Scan process can reduce the backup of that volume by almost that same amount of time. As the night goes on, those savings will add up and it should allow you to back up more computers. The amount of time used to actually copy the data and save your Snapshot will be about the same as it was with prior versions of Retrospect.

Benchmarks from our own internal testing showed performance increases from 35-50% for incremental backups (with client backups averaging about a third faster and local backups almost halved. Thus, if an incremental backup would have taken two hours per computer before using Instant Scan, with Instant Scan you would expect the backup to finish within an hour and twenty minutes. This means you should be able to backup three computers for every two that you could do before (3 x 1:20 = 4 hours). As with all such benchmarks, your mileage may vary.

Last Update: May 15, 2018

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