How to permanently archive Time Machine backup? I have an external hard drive where my Time Machine backups are located. My OS is El Capitan.

I would like to permanently archive this entire TM backup and move it to another hard drive, and it would be best to archive these backups to a compressed disk image.

I have tried to archive the Backups.backupdb folder with SuperDuper! and Carbon Copy Cloner. CCC copies files to DMG but Backups.backupdb is only 161 GB in size, and CCC has supposedly copied 190 GB, which has me thinking something is wrong.

I have not yet tried to create a ZIP archive or a DMG (using Disk Utility).

How can I create a DMG to archive Backups.backupdb to another hard drive?

More info:

Thanks for help.

I tried to make DMG using Disk Utility.

After 6 hours, Disk Utility got error: Operation failed with status 2.

Creating "TM BU" dialog, "hide details" window was empty during 6 hours.

I used read/write format because i'm planning to index DMG with Spotlight after DMG is created if that's possible.

sudo mdutil -i on '/Volumes/TM BU' user name "name" password "password" with administrator privileges

Then if possible convert read/write DMG to compressed.
I would recommend using hdiutil to image the disk.

First, run diskutil list in the Terminal to see the identifiers for each disk. You'll want to note the identifier for your Time Machine drive (format is /dev/disk#).

Then, in the Terminal, use:

/usr/bin/hdiutil create -srcdevice /your/disk/identifier -format UDZO name.dmg


Where /your/disk/identifier is the /dev/disk# corresponding to your Time Machine drive, and name.dmg is the name of the output DMG. The UDZO format is the default compressed disk image format. The disk image will be a replica of the entire USB drive.