Performance & Partition Questions

Partitioning a drive has no effect on performance.

You will get the best performance if your startup drive is not partitioned such that user files & system/application files are on different partitions -- this just forces the drive to perform longer seeks on the average to go between the two partitions, puts one or the other's files on a slower part of the drive, prevents one or the other's small files from being automatically defragmented & clustered by the OS, etc.

The first thing to do is make sure you have adequate free space on the drive, at least 10 to 15% of its total capacity. Then run Disk Utility's Verify Disk & Repair Permissions functions to make sure it is healthy.

Beyond that, we need to know what performance issues you are having since there are many kinds of performance problems & different solutions for each of them.

The reason partitioning sometimes helps is to isolate the system to the first half or third of a drive; to use the rest of the drive for non-system uses.

The only way I know that has worked (for 40 yrs) is the backup-format-restore.
SuperDuper omits temp files and caches that are best created new; organizes directories; consolidates free space.

I don't even touch the apps you use for maintenance. If you want a recommendation, SuperDuper and Disk WArrior alone or at top of list.

For some apps and systems, 1/3 free space is a must; for others, 24-32GB of free unfragmented space is a minimum.

You may just need a larger new (and therefore faster) hard drive; or to use FW800 or ExpressCard if possible.

40 GB of free space out of your 320 GB HD seems like you are starting to crowd the minimum requirements. You did not state how much RAM you have installed. Things will slow down if there is not enough HD ! Free space and RAM make a huge difference.

macera:

To reiterate a few points made by previous posters:
• You need to maintain a minimum of 15% to 20% of the total capacity of your HDD as contiguous (unfragmented) space. If you are working with large video files that should be closer to 20% to 30%. 40 GB is not sufficient available disk capacity on a 320 GB HDD.
• Partitioning the HDD will not help, and may hinder in the objective you seek.
• For the work you are doing you should consider 1) Getting a larger capacity and possibly faster HDD such as a 500 GB 7200 rpm. 2) Maxxing out the RAM in your computer. Alternatively you may want to try to store and work with those large video files on an external firewire 800 drive and see how that works for you.

😉 cornelius

cornelius wrote:
• You need to maintain a minimum of 15% to 20% of the total capacity of your HDD as contiguous (unfragmented) space.

Why do you say this free space needs to be contiguous? Current & recent versions of OS X do not need a contiguous space for VM, which is paged in & out in small chunks anyway. Large video files play perfectly well even if somewhat fragmented since they are buffered & the required data transfer rate is far less than even a moderate performance SATA HD is capable of delivering.

Try this: open two different video files in QuickTime Player & play both simultaneously. Note that at least on reasonably fast Macs neither one jitters or drops frames. Since the two files cannot be in the same contiguous space on the drive, it is obvious that a single video file can be fragmented without affecting playback performance.

An exception to this is editing multiple realtime streams of uncompressed high definition video, since their combined required data rates may exhaust buffers, but this is rarely attempted using a single drive since it would likely exceed the sustained transfer rate of the drive whether or not the files were fragmented.

Why do you say this free space needs to be contiguous?

As I understand it, space does not need to be contiguous until your HDD reaches the critical limits. Apple acknowledges that as one of the conditions in which defragmentation may be helpful:

If your disks are almost full, and you often modify or create large files (such as editing video, but see the Tip below if you use iMovie and Mac OS X 10.3), there's a chance the disks could be fragmented. In this case, you might benefit from defragmentation, which can be performed with some third-party disk utilities. (See: About disk optimization with Mac OS X ).

However, more important than available capacity for processing video files is the need for contiguous space for swap files, and for directory expansion. Without sufficient space for growing the Extents Overflow file you end up with extents with existing data being over-written, directory corruption, file corruption and possible data loss.

Note, again, that with sufficient disk capacity all of this is cared for by OS X doing this automatically as described in the article linked above, thus the critical need for maintaining a safe buffer of contiguous free space to avoid serous issues.

😉 cornelius

However, more important than available capacity for processing video files is the need for contiguous space for swap files …

As I mentioned, this is not an issue with current & recent versions of OS X. The gory details are explained in Kernel Programming Guide: Memory and Virtual Memory, Memory Usage Performance Guidelines: About the Virtual Memory System, & related references but basically, VM swap files are mapped into small 4 KB page segments all of which do not have to be contiguous, although this typically improves performance. Swap files are also small, starting at 64KB each, which helps them fit into available spaces on the startup drive.

Without sufficient space for growing the Extents Overflow file you end up with extents with existing data being over-written, directory corruption, file corruption and possible data loss.

I've heard this mentioned as an explanation of why directory or file corruption might occur, but frankly, it is extremely unlikely in recent versions of OS X unless the volume is already extremely full & extremely fragmented. The gory details of why this is so are explained here, but basically it is because the entire "Metadata Zone" takes precedence over ordinary files, so there is almost always enough room in it for the Extents Overflow & all other related HFS+ file system "housekeeping" file additions for any new files you can fit onto the drive.

R C-R:

Thanks for the links, which I will peruse later today. As I noted earlier, the contiguous space becomes critical when the HDD becomes too full. A definition of too full seems elusive. I go by a study done my Micromat done a while ago, for which I have lost the reference, in which they found that more than 85% is where directory corruption begins becoming a problem. That may have changed with newer OS and newer disk and data management, but I have not seen anything that would controvert the Micromat findings. If you are aware of such data I will be glad to see it, as I am always seeking to deepen my understanding.

😉 cornelius