By default, most computers come with one partition and one volume on that partition. Well, in OS X there’s also a recovery partition, but that’s hidden so we’ll pretend like there’s just one. You can create additional volumes, which are useful for a number of different scenarios. The operation of creating partitions usually involves resizing a partition. That can be somewhat dangerous, so make sure to backup your Mac before doing so. To create an additional partition (and by default an HFS+ filesystem on that partition), first open Disk Utility from /Applications/Utilities. Screen Shot 2015-12-08 at 11.21.47 AM Note that by default, the boot volume is highlighted. You can’t create a partition inside a volume or partition, so click on the name of the disk above that. Screen Shot 2015-12-08 at 11.21.52 AM Here, you can choose to run First Aid, Erase, Mount/Unmount, and Info. Most are unavailable when clicked on a disk, so let’s click on Partition. Doing so shows you each partition on the physical disk. Screen Shot 2015-12-08 at 11.21.57 AM You can click on each partition to see information about the partition. Let’s click on the plus sign (+) to create our new partition. Screen Shot 2015-12-08 at 11.22.11 AM When prompted, provide a name for the partition. You can choose a different format for the partition, but let’s leave that as the default for now. Then enter a size and click on Apply. Screen Shot 2015-12-08 at 11.20.00 AM If you’re taking space away from a partition, the old partition will be resized as a smaller partition, provided that there’s enough free space to do so. Screen Shot 2015-12-08 at 11.20.05 AM   Once the process is complete, you should see your new volume mount.    

Someone hands you a USB drive. You put it in your computer and you can’t access anything on it. You are running an imaging lab and you want to backup or troubleshoot a device before you re-image it, but you can’t access certain files. Obviously, you can sudo. But, you can also simply disable permissions on that volume (which, like getting someone to make you a sandwich, requires sudo of course). The command used to enable and disable permissions on a volume is vsdbutil, located at /usr/sbin/vsdbutil. And there’s a LaunchDaemon at /System/Library/LaunchDaemons/ that interacts with diskarbitrationd so that when a volume is mounted, it is marked as having permissions activated or deactivated (which is basically “Ignore Permissions” at the Finder). To use vsdbutil to enable “Ignore Permissions”, use the -d flag followed by the path to the volume: sudo /usr/sbin/vsdbutil -d /Volumes/Myvolume To then enable (or activate, thus the a) permissions again, use the -a flag: sudo /usr/sbin/vsdbutil -a /Volumes/Myvolume You can also run the -c to see the status for a given path: sudo /usr/sbin/vsdbutil -c /Volumes/Myvolume And last but certainly not least if you’re working on a lot of volumes, the -i option will enable permissions on all mounted HFS and HFS+ volumes: sudo /usr/sbin/vsdbutil -i Overall, it’s very easy to send these commands using a positional parameter (e.g. $1) to a script, performing a mount, some operation (backup, reimage, restore, repair some corrupted data, etc). Note: You can’t Ignore Permissions of FAT or FAT32 volumes using the command line or a Finder Get Info screen.

Back when I worked with Xsan a lot more than I do now, one of the things we spent a lot of time doing was working with metadata and journal data on Xsan volumes. You can also view journal data for non-Xsan volumes. The hfs.util binary is used to view journal data about volumes. In this example, we’ll look at the journal size and location the boot volume of our system: /System/Library/Filesystems/hfs.fs/Contents/Resources/hfs.util -I /Volumes/Macintosh\ HD The output shows the size of the journal and the location, as follows: /Volumes/Macintosh HD : journal size 40960 k at offset 0x1a38b000