Changing size of two partitions

You can freely resize partitions using Apple's provided Disk Utility application but it cannot move the +start of a partition+. IOW, Disk Utility can't move the starting point of your partition C "up" into the space made available by making partition B smaller.

There are third party utilities that in effect can do this, but they actually involve moving all the partition's files from one part of the disk to another so for safety's sake all of them strongly recommend making a backup of all the partitions on the drive beforehand. That's because changing the drive's partition scheme data & moving around so much data on it cannot be made 100% bulletproof so there is always some small but non-zero chance that the process will fail & you will be left with a drive that must be reformatted to again become useable, making all its previous data unrecoverable by normal means.

Because of this need to back up everything (which is true whether or not you want to repartition anything), & because these utilities are relatively expensive, I think it is usually simpler & better to invest in a backup drive, clone the partition(s) that you want to move to it as needed, delete those cloned partition(s) on the original drive, create new one(s) with the sizes you want, & then clone back the original content from the backup clone(s).

So for example, you could resize partition B smaller, clone partition C to your backup drive, delete C from the original drive, create a new partition C starting at the end point of B, & clone the backup of C back to it.

I recommend a hard disk case and make your profile backup and creates the partitions from scratch a pro system and the other a 50GB size that remains, after this backup to restore your profile

Greetings,

Use iPartition - It works well, and I have used it for many years. You can resize any part of your drive, including the boot drive. It's cheap, as well - http://www.coriolis-systems.com/iPartition.php

Cheers,
M.
*****

Danielle Kamp wrote:
Hi,

I have 3 partitions on my computer. Let's call them A, B and C with A = primary boot, B and C are just data.

That's rarely a good idea. OSX works best with everything in the same partition of a single drive. With the data and free space divided up, performance won't improve, and may very well be degraded.

It guarantees longer seek times, as the drive head must move across the free space when going from one partition to another.

If you guess wrong about the sizes, you can either waste free space on one or more partitions, or have too little, increasing fragmentation and slowing performance.

Also, OSX's +Adaptive Hot File Clustering+ feature can't move data from the data partitions to the OSX volume if it would be more efficient there.

Separare drives are very different from separate partitions on the same drive. That usually is a good idea, and usually will result in better performance. 🙂

The reason is, each drive has it's own access arm, moving independently; different partitions on the same drive are accessed by the same one.

You should have OSX, your apps, and user home folders on the OSX drive, usually with at least 15% to 20% free space (more is usually better). You may want to move some things that are normally in a home folder to a separate drive, such as your iPhoto and/or iTunes libraries, and video files.

Your other drive might work well with separate partitions, unless they tend to be accessed frequently at the same time. But if you regularly use, say the Reference images in your Projects, the access arm will have more miles on it than the Space Shuttle if they're in different partitions (pardon the slight exaggeration 😉 ).

OSX uses "Adaptive Hot File Clustering" on the OSX volume; it will actually move things that are often accessed to the fastest part of the partition, and things that are frequently accessed together to the same part of it, and adjust that as your workflow and habits change. I'm not sure if that's done on a data-only drive as well.

If you do have stuff in those partitions that isn't used much, put it in the partitions towards the bottom of the diagram that Disk Utility presents; that's the slowest part of the disk. See #1 in [Formatting, Partitioning, Verifying, and Repairing Disks|http://web.me.com/pondini/AppleTips/DU.html] (or use the link in *User Tips* at the top of the +Using Snow Leopard+ forum) for a sample.