Data Backups
Data backups refer to the collection of regular, automated copies of data files to an independent storage system. Backups are the first line of defense in protecting your data from loss, corruption, disasters (human-caused or natural), and other problems. The more automated the process and the more independent the storage system, the greater security afforded to your data.
| Data Security | Level of Automation | Storage System |
|---|---|---|
| Least secure | Backup requires that you plug in a USB drive and manually copy files. | USB flash drive you carry with you. |
| Backup software automatically starts backup when USB drive is connected. | USB hard drive that is stays at home. | |
| Backup software schedules backups when you are on your home network. | Network hard drive at home. | |
| Most secure | Backup software schedules backups as long as you have an internet connection | Network hard drive at a remote location. |
Types of Data Backups
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Full Backups - Each backup is a full copy of all data to an independent storage device.
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Incremental Backups - Copies only the data that has changed since the last backup operation of any type. The first backup must be a full backup.
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Differential Backups - Copies all data that has been changed since the last full backup. The first backup must be a full backup, and any subsequent differential backup will refer back to that full backup.
The full backup takes the most space, but recovery operations require only a single file. The incremental backup uses the least amount of space, but recovery operations require the full backup and all incremental files made since the full backup. The differential backup uses an intermediate amount of space, but recovery operations need only the full backup and the most recent differential backup.
More details can be found at the page Types of backup explained: Full, incremental, differential, etc.
Backup Systems at Purdue
Home Directory or Network Drive
Your home directory, typically mounted as the U: drive on Purdue maintained Windows machines, is the
focus of regular, automated backups. Purdue pays for this, and you cannot stop it. Note that this DOES
NOT apply to disks installed on your local computer, such as the C: drive, a scratch (or D:) drive.
Note
The C: drive should only contain the applications installed locally. A scratch drive, if present, is
provided to facilitate working with large files on Windows software (say with ArcGIS or AutoDesk), and those
files will not be available to any other machine, nor will they be backed up.
To recover files from the backup of your home drive, please refer to the latest instructions from Purdue IT.
Note
You will probably have to click on "Show more options" on the menu that opens when right-clicking before you will see the command "Restore previous versions" describe in this document.
RCAC Data Depot
The data depot is not a full backup system, but instead data is fully mirrored with regular snapshots.
This means that there are two copies of every file at all times (some apps cannot distinguish the
duplicates so it may appear that your storage is two times what you are expecting, e.g. with the Linux
du command). Snapshots are similar to full backups, but tied to a different capture and storage system.
To recover files from the snapshots, please refer to the latest instructions from Purdue RCAC.
Note
I have not found the operating rules for RCAC snapshots on any of their pages, so here is what I have gleaned by looking at the manual listing of snapshot files. Snapshots are collected at once per day (overnight). RCAC maintains daily snapshots for about eight days. They appear to maintain weekly (Monday) snapshots for the previous four weeks. They maintain monthly (first day of the month) snapshots for the previous three months (not including the current month). So you have roughly 90 days to recover files before the snapshot is reset.
The snapshot does not capture change data, but is instead a copy of the file as it existed when the snapshot was captured. This works well for files that have been untouched on the system for weeks or months, but less well for files that are regularly being modified. Of course, you are more likely to notice the loss of a file you use regularly before the daily snapshots start to be deleted. goes missing or is corrupted and when the resovery happens, the bigger the gap between
Other Systems
If you are using a Purdue maintained system other than the ones described, say one that it maintained just for your research group, refer to your local System Administrator for guidance on what is backed up and how to recover lost files.
Personal Computer Backups
Establishing a robust, automated backup system for your personal computers will go a long ways to preventing the sinking feeling you get when your hard drive fails with the only copy of your dissertation. Or when you discover the USB hard drive that contains your nearly completed analysis is not on your desk when you arrive at work in the morning. Or when lightning strikes near your apartment and the surge fries your computer motherboard.
I know that all of these events have happened.
When deciding on a home backup system, consider your finances and your tolerance of risk. Also consider following the 3-2-1 rule of backups, which includes three copies of your data on two different media, with one copy off-site (not in the same physical location as the source). Remember that you have access to Purdue networked storage and Depot storage, but those do not help if you choose to take you work off-line and home. Purdue also spring for OneDrive storage, which also provides a secure place to keep your files.
Home-based Backup Systems
There are very good automated backup programs available for free or relatively inexpensively, including: - Time Machine, which is installed with the Mac OS X operating system on any Mac computer or laptop, - Windows Backup, which is included with Windows 10 and 11, - And many more that will be reviewed annually by PC Mag and other reputable on-line resources.
These work best when coupled with a networked drive (or Network-attached storage (NAS)) located on your home network. Buy one with sufficient space to backup all of your computers, and make it available over your home WiFi network so that systems can be scheduled to backup files automatically - when you first get home, or overnight when you are not using it (just make sure the system is plugged into power so the backup can start).
As of 2025, a 1 TB, single drive NAS is selling on Amazon for about $100. For more security, you can purchase a RAID drive system that will mirror files across two or more disks, to shield against disk failure.
Cloud-based Backup Systems
There are also many good cloud-based backup systems. These are different than syncing files with OneDrive or other cloud storage solutions, where you work with files in folders on the cloud drive. Make changes or delete a file, from the cloud drive and it is recoverable for a while but that time will be limited (see the service contract). Cloud-based backup systems, are applications running on your system that do regular incremental backups to cloud servers. This means that they can work anywhere there is a network connection (not just on your home network), and generally they work in background constantly updating your backup so that when you need it, it will be there. The backups should be encrypted and accessible only to the account owner (read the fine print).
Dr. Cherkauer has used Carbonite to secure his family's computers for years, but there are many other services. Again read reviews from reputable sources (not just the hype from a specific services page), and select a package that works for you.