Runs4food--
You ask an excellent question. Your post touches on two topics--namely, how Mozy handles external drives and how Mozy's quota and retention policy works. I'll address the quota/retention issue first.
Mozy will retain all file versions backed up between the dates of 30 days prior to your most recent backup and your most recent backup. Expressed mathematically, if N is the date of your most recent backup, then all file versions between N and N-30 will be available for restoration. Unfortunately, a lot of customers are under the impression that we retain files only 30 days from the present; that's not the case. Below are a few sample scenarios representing common use cases:
1) On July 1st, you delete your 1Q 2010 data, thinking you'll no longer need it. Mozy continues to back up daily. On July 10th, you realize you need some of it back. Using the "Search All" or July 1st backup date in the in-client restore, you're able to restore the files you deleted.
2) On July 1st, you beging backing up your Quickbooks financial data. On July 10th, an embittered employee of yours begins making extreme changes to your data, rendering it meaningless. Mozy, again, continues backing up daily. On July 20th, the aberrancy is noticed, and you begin making an effort to find a good version of the file. Your most recent backup contains a corrupted version of the file, but going back, you can restore good versions from July 10th or prior.
3) On July 1st, you're offered a consultancy position overseas where Internet access is limited. You continue making twice-daily backups until July 31st, when you put your computer into storage and fly out. You return on December 1st; when you go to retrieve your computer, you realize that your storage unit has been broken into and your computer stolen. You'll still be able to restore data from July 1st through July 31st (all 60 versions), because both dates fall within N (most recent backup) and N-30.
4) On June 1st, you delete your 2009 tax info, concluding that it will no lenger be needed. Mozy continues to perform daily backups. On July 15th, the IRS informs you you will be audited this year. You wish to retrieve your 2009 tax info, but it's not there-- June 1st is 45 days prior to your most recent backup, and thus outside the retention policy.
Note, however, that we err on the side of caution in our garbage collection policies, and thus there is a good (or excellent) likelihood you'll be able to recover data outside the 30-day retention window.
Your screenshot indicates that the amount of data Mozy is backing up varies dependent on whether or not your external hard drive is attached. That is true. Mozy, when calculating quota used (what you see in your attached screenshot), uses only data from the most recent backup. For users who are quota-limited (MozyHome Free, MozyPro), it has to be this way in case the user needs to return his or her backup to within the defined quota. Another example:
---You have a SQLExpress database on your computer that is 10GB in size and 5GB of other static files to backup. Every day, the database undergoes 1GB of change, but only grows by 500MB (the other 500MB in change occur in parts of the database that are being overwritten). After 30 days from your initial backup, the following are true:
a) Your quota currently being used is 30GB (10GB database initial + 15GB of growth+ 5GB static)
b) Mozy actually has 45GB on disk (10GB database initial + 30GB of change + 5GB static)
c) If you delete your database today, your quota used will instantly go down to 5GB. However, you will still be able to recover the database for another 30 days.
In your case, even if your most recent backup did not include the external drive (and therefore reads as 22GB backed up), you will still be able to recover data from it. You can test this yourself. Disconnect the drive, run a backup, and then open up the in-client restore application, selecting "Search All"." You'll still be able to recover data from the external.
Now, as to why Mozy looks like it has to back everything up if the drive is disconnected during a backup. Mozy uses a file system filter driver to monitor your file system for changes. This allows us to ensure that any changes made to your files are captured and that backups occur differentially (we're not backing up your whole file selection every time; we're only backing up what's changed). However, when an external drive is unmounted, we can no longer monitor the changes made to it; thus, a full re-scan is performed whenever an external drive is remounted. When Mozy actually goes to back up the files, it will initially perform a comparison between what's stored on the drive and what's stored on the server; when matching files are found, they are not uploaded. This process must be performed for each file individually, however, which may take some time depending on the number of files you have. Another example, if you'll permit the indulgence:
You and your business partner work in a graphics & media firm. In order to expedite your work, you share an external drive and pass it between you when large files need to be transferred. You use Mozy to back this external drive up. Every project is assigned its own folder, and generally you only work on one or two projects at a time. On July 1st, you execute a backup with the external drive attached; projects G and H are your current active projects. On July 2nd, you hand the drive off to your partner; backups continue to execute normally. The backup of July 2nd indicates a backup size of about 80GB less than is the norm because the drive was not attached. On July 3rd, your partner returns the drive, and Mozy executes another backup. It compares the files in folders A, B, C, D, E, and F, and finding no changes compared to what's currently stored on the back end, skips uploading these files. It does detect changed files in folders G and H and, because it couldn't capture the difference, uploads the changed files in their entirety. On July 4th, you give your partner the drive and execute another backup; again, the total size backed up goes down by 80GB. You realize on July 4th that your partner has made a rather serious error with project H, and you need to retrieve a version prior to the time when your partner made his changes to it. You open up the in-client restore application, select the July 1st date, and restore the version of the file you need.
I realize this is a lengthy post, but I hope it proves to be informative for users an potential users of Mozy who may have questions surrounding our retention, quota calculation, and external drive backup procedures.
