Capacity?

[michelmueller]

I am a little bit confused about the capacity of my new VXA-2 drive (80 Giga uncompressed).

I just did a backup of my NT-Server. The Windows Explorer told me of total 76 Gigabyte on my Drive.

During the compare activities I was told

Remaining 39,6

Completed 17,2

 

Comes the difference from that view, that the "Rameining/Completed" tells me the hardware compressed files?

 

Michael Müller

[AmyJ]

In many cases, the number of files Retrospect shows to you will be the same as what you would see if you viewed Properties on the same data set in the Windows Explorer. There are times, however, when the file counts and sizes reported will differ. These differences are intentional and easily explained.

 

The file count figures that Retrospect reports (for example in the operations log) are based on the files that Retrospect will actually back up. If you are backing up a system volume (e.g. the drive with your "Documents and Settings" folder under Windows 2000 or XP), Retrospect excludes all of the registry files, because it backs up the registry via Windows registry APIs, rather than on a file by file basis. Further, Retrospect excludes virtual memory swap files, and other files that should not be backed up, per Microsoft's recommendations. The Windows Explorer, on the other hand, includes all registry files in file counts. The Explorer also may or may not include hidden files in its counts, depending upon whether or not you have it set to show hidden and system files.

 

To give a specific example, on a freshly installed Windows 2000 Professional system, Retrospect reports 8403 files to be backed up, while the Explorer shows 8466 in the Properties window for drive C:. This is normal, provided you are using Retrospect's All Files selector (and that you have not modified the selector from its default). Retrospect is backing up all files that need to be backed up.

 

Retrospect and the Windows Explorer can also differ in the size of reported items. The discrepancy in size is due to the difference between any given file's logical size and its physical size. The logical size of a file is the actual number of bytes the file contains. The physical size is the amount of space the file occupies on a hard disk or other volume. This physical size varies for a given file depending upon where you store the file. Retrospect reports a consistent size based on the logical size of a file, regardless of where you store the file.

 

Retrospect has its own fixed internal allocation block size of 512 bytes. Specifically, Retrospect rounds the file size in bytes up to the nearest 512 byte boundary and then rounds up to the next even kilobyte (K) to report what you might call the "Retrospect size" of a file. This means that when Retrospect backs up a 1 byte file, it will report the file as using 1K in a Backup Set or Browser.

 

Further, a file uses different physical space depending upon the volume where it is located. Hard disks can be set to use different block sizes, and a 1 byte file will use at least one allocation block, which might be 2K, 4K or more.

 

In general, when you are backing up, Retrospect shows the Retrospect size of the file in browsers, the log, and the execution status window. When you are restoring or duplicating, Retrospect uses the Retrospect size in the log and execution status window, but the physical size calculated using the destination volume's minimum block allocation size in the summary window.

 

In the end, the file count and exact size reported will rarely, if ever, agree exactly between Retrospect and the Windows Explorer. This does not indicate a problem, and is in fact proper functioning. Should your counts be different by a large margin, you should review the selector you are using to choose files, and verify that it is indeed marking all of the files that you wish to back up.