Need partitioning advice

I heard that Mac drives don't need partitioning.

All Mac drives need at least one Partition. This is where you select the Partition Map Scheme, which for Intel is GUID. Choose a Partition Scheme from "Options." (This is left out of the Leopard instructions.)

http://www.kenstone.net/fcphomepage/partitioningtiger.html

Instructions are for Leopard (and Tiger, with much valuable information there, as well) but remains pretty much the same for Snow; but see note above about selecting a Partition Scheme from Options.

Message was edited by: WZZZ

Partitioning won't really gain you anything and it's useless to make a separate partition for a Photoshop scratch disk on the same physical drive where Photoshop and the operating system live. For best results, use a different drive altogether for the swap disk. The point of doing that is so that when Photoshop is reading/writing to the swap disk, it's not competing with the operating system or other processes that may be happening on the system drive. I gave up partitioning years ago when the price of storage came down enough that I could use separate drives for applications and data. I keep only OSX and applications on the main drive, use a separate ExpressCard SSD for Photoshop's swap disk, and a collection of external USB drives for data. (I don't do video editing, which would require a much different setup.)

There is generally no reason to partition the startup drive with more than the default single volume configuration. Creating multiple partitions on a single drive does not by itself increase performance or security; in fact, it can easily decrease performance if frequently accessed items (like the OS & user files) are on different partitions of the same drive because it significantly increases average seek times. It can also result in increased file fragmentation in other than the startup (OS) partition because that is the only partition the OS automatically defragments small files on.

It also means there is proportionally less free space for the OS partition to use for VM & temp files, which can result in erratic operation & even data loss if it runs out of free space.

I partition HDs because I run various incarnations of the OS. However, I don't separate applications from those volumes. I also have separate volumes for user-created documents, e-mails, and disk images of installers and updates. Additionally, I have ext FWHDs that mimic what's on the internal HD; that is, bootable clones and backups, which I keep current on a frequent basis. Your' plan's fine as long as you routinely backup those volumes with at least one FWHD.

All Mac drives need at least one Partition. This is where you select the Partition Map Scheme....

My bad. You can get to Options to set the Partition Map Scheme from "Current," without needing to set a partition first.

Also keep in mind that if you are tempted to keep the bulk of your user document files on external drives & are using an iMac, their accessibility will be limited by the speed of your USB or Firewire interface, which is considerably lower than that of the internal SATA bus. This will be more evident for small files that fit into a drive's buffers & thus are limited by the maximum transfer rate of the interface more than by the sustained transfer rate of the drive itself.

This means it is usually better to keep your home folder on the internal SATA drive so that frequently accessed small files like many plist, application support files, & the like benefit from that & reserve the external FW or USB connected ones for large & less frequently accessed document files.

WZZZ wrote:
My bad. You can get to Options to set the Partition Map Scheme from "Current," without needing to set a partition first.

Do you mind telling me how you can do this? On my Macs at least, the "Options…" button remains greyed out as long as "Current" is showing in the Volume Scheme popup.

Reread my post. AFAICT, there's no performance hit using partitions on the internal HD. I also have a 10 GB partition that holds a bootable copy of the OS X install disc, so reinstalling doesn't get slowed down by using the original DVD in the optical reader. The paramount thing is to have multiple backups, bootable ones for the OS.

1. You don't have to erase user created files to reinstall Snow Leopard; in fact, you must take a special step to do so by first running Disk Utility to erase the drive.

2. Functional HD's are always partitioned. Even when Disk Utility or Finder only shows you a single partition, there is at least one other hidden one & sometimes more. This is necessary for normal operation & should not concern you, other than if you refer to a drive as 'non-partitioned' it means an unformatted one & this is what many users will think you are talking about.

3. There are a few valid reasons to partition the normal (internal) startup drive in an iMac, but improving efficiency is not among them. Examples have already been given for why you might want to do this, like to have more than one version of an OS on the drive. If you do not intend to do that or something similar, there is no reason to create any additional partitions.

In your case (from what you've told me so far) the only partitioning arrangement that would make
sense would be to partition your drive into 2 partitions.

The first (beginning partition - at the front of the disc) would hold your operating system and
allow enough space for your normal Apple Supplied apps and a photoshop scratch folder.

Due to the way modern disks are formatted, the fastest data transfer occurs at the beginning
of the disk (zoned bit recording). The raw data transfer rate (sometimes called the media transfer
rate) of the disk when reading the outside cylinders is much higher than when reading the inside
ones.
http://www.pcguide.com/ref/hdd/geom/tracksZBR-c.html

Place your user account on the data partition. Be sure to keep at least one spare admin account
on the boot drive (first partition).

Install personal third party apps in your home folder to save space on the boot drive. System
wide (for other users) apps should not be installed in your home folder though.

baltwo wrote:
AFAICT, there's no performance hit using partitions on the internal HD.

It depends on what is on each partition, how often the files of each need to be accessed, & how much of the drive each partition occupies. For instance, if you were to put the OS (/System/, /Library/, /Private/, & so on) on one partition & the user home folders on another, the drive will have to transverse longer average seek distances when accessing files in one partition after accessing those in the other. Since normal use involves frequent access of some files in each partition & longer seeks take proportionally longer times to do before data can be read, this can cause small but noticeable decreases in the responsiveness of the system.

AFAICT, it's too small to measure accurately and I've not noticed it, especially with the two iMacs (the other being the 24" one I just gave to my mate).

KJK555 wrote:
Place your user account on the data partition.

I think this is a bad idea for the reasons already mentioned. It significantly increases the seek times when files have to be accessed from one then the other partition, prevents automatic small file defragmentation in user account folders, & so on.

And since you mentioned it, it also forces all user account items (including caches, application support files, & everything else in ~/Library/) into the slower, lower density middle zone of the drive.

It is debatable just how much all this lowers overall performance but it certainly does do that.

I have to agree with you Baltwo:
As long as the files are not badly fragmented, the seek times are not the largest factor in moving
data around. Read ahead disk caching minimizes negative affects of disk seek times. The most
predominate factor is usually the data transfer rate (at least with larger files).

Operating system files are the usually the files affect the most by average seek times because they
are small and accessed much more frequently and in much greater numbers than data files, except
in a data server such as a www server or corporate business server.

Keeping the system files "captured" in the front most part of the platter by partitioning, decreases
overall seek times and increases data transfer rates of system files, thus increasing performance. By
preventing system files from getting written to slower parts of the platter, as commonly happens
during software updates.

On a single partition, previously written data files get in the way near the front of the drive,
forcing system files (usually during an updateprocess) to be written on a slower part of the platter,
decreasing responsiveness of the OS.

Also, as R C-R points out, moving the user folder to a slower partition can effect performance
slightly, but there is a way around that as well, leave your user folder on the boot volume, then
simply move your documents folder to the data partition, and symlink it back to the user account.
I have used this arrangement for years. I can't recommend it to someone who can't get used to
the idea of splitting up their data from their user account.

I have my data split up over 12 volumes and 4 internal disks (not counting my external disks).