Here's the deal: I have a Macbook Pro 6,2 – I think late 2010 model. I have two mismatched drives with the same speeds. A 750GB Momentus XT, that SSD HDD hybrid, and the Seagate Momentus 500GB. Both are 7200 RPM. I replaced the optical drive a while back with a HDD.

I want to install the most opportune parts of the operating system to a separate applications folder, therefore prioritizing on the outer edges of the disk – specifically files that will be run more often therefore they can be accessed quicker.

However in addition, because they are mismatched in terms of GB per disk, I have a setup that I would like to use that further optimizes it.

Basically the first disk is separated into 3 partitions (values approximate):

  • System: 50 GB
  • User: 200 GB
  • RAID: 500 GB

Using Mac OS X' built-in software RAID, the RAID partition will be RAIDed with the second disk being the 500GB disk. Therefore it appears as three disks: a system disk, a user disk, and a RAID disk.

However, I would like to separate the applications as well by partition – specifically by priority. System ones of course get high priority, granted I would like to move specific applications out of the Applications folder (honestly a lot of them like Photo Booth and FaceTime aren't really that helpful), however for the intent of this question I would like to know if the system can recognize and move the system folder as a whole to a separate drive, leaving just the system on the system partition.

Ideally, I'd like:

  • User preferences and Library on the system partition.
  • The user applications on the user drive for general things like Photoshop, Aperture, or Lightroom.
  • System applications on the User Drive
  • A special applications folder on the System Partition for high priority ones like Final Cut Pro, or Autodesk Smoke, things that will be accessed alot or use alot of reading and writing.
  • The User files and folders – you know, Documents, Pictures, etc. – on the RAID drive, along with a specific applications folder there as well for less used not as high priority applications such as optimization applications or smaller things like disk space programs etc. Text editor, or Espresso things like that, that don't need the speedier read and write.

Therefore, in theory, the applications and system files used most often will be prioritized at the disk edges and therefore perform better, and if all goes well, it'd make Launchpad work nicely with all of this.

I know most people's answer would be to buy an SSD which I'd really love to do, however it's not in the budget and since it is a MacBook Pro, space is limited. I'm trying to maximize storage with performance as well.

  • How much speedup would putting things at the disk edge produce? and how much speedup would make a difference to you. Also doesn't the large cache on the Momentus drive make these measurements irrelevant the speed of something in cache is much quicker than any difference as to where the file is
    – mmmmmm
    Mar 23, 2013 at 7:24
  • That is unfortunately what I do not know. As far as I can find nobody has tried this therefore there are no benchmarks in regards to system performance. However there are indications that edge data does speed up i believe its the iops possibly or the read and write access of the outer edges of the disk. Just in this combination, unless someone has benchmarked previously there is no way to know. In theory it seems sound. Im using my macbook pro as a video editing platform therefore any speedup possible is helpful. Mar 23, 2013 at 17:37
  • I think OSX does move files around as it sees fit and as far as I know anydifference will not be noticeable
    – mmmmmm
    Mar 23, 2013 at 17:42
  • Osx does auto defragmentation, however constraining the individual partitions will basically bottleneck certain files and folders by priority. Therefore, the most important ones i.e. system files, and application files, will be prioritized by partition first, then mac osx will prioritize the individual ones within the partitions. Mar 23, 2013 at 17:44
  • But the momentus SSD will cache things so making any measurements difficult and probably meaning less as to the position
    – mmmmmm
    Mar 23, 2013 at 17:46

1 Answer 1


Haven't tried all of the things you are asking, but I have succeeded in moving /users to another partition. Mount it as /Volumes/Users, and make sure there is symbolic link from /Users to /Volumes/Users.

There is a bit of a dance: Login as root. Sudo doesn't work for this. mv /Users /UsersOld mount newdisk /Users copy /UsersOld/* /Users for each user: chown -R his directory.

You may be chasing down ACL issues for a while.

You may be able to do the copy with tar. e.g. cd /UsersOld; tar -cf - . | tar -C /Users -xvf -

This will do the right thing for permissions, but I don't recall if it does the right thing for resource forks and ACLs.

You may need to mount it at a different point, creating an appropriate fstab file with an entry for it.

I would suggest that you enable root as a login account so you can have a GUI to snurfle around when things go pear shaped.

As to the efficacy of what you are doing: It won't make much difference. The read/write performance of having stuff at the edge vs spread out isn't much. You're talking at best 20% or so, and more likely far less.

If you have not done so, max out the ram your laptop can hold. This does far more for increasing performance than any other upgrade you can do, especially if you are using data pigs like photoshop.

  • Yes it seemed that setting the fstab was an option, along with symbolic linking. The only fstab tutorial i could find that dealt with this was very old leopard/ snow leopard tutorial and that one seemed more concerned with making a separate swap partition which im not bothering with here. Symbolic linking seemed promising, however it also makes it seem just a bit too easy. Mar 23, 2013 at 17:30

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