Need partitioning advice

KJK555 wrote:
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.

Nope. User domain files, especially those in ~/Library/, are quite often as frequently accessed as those in the system domain. This is especially true in ~/Library/Caches/ & ~/Library/Preferences/ByHost/.

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.

As long as files remain in the same zone of the drive, there is very little difference in access times as long as they are not badly fragmented, which would easily dominate the effects of faster vs. slower zones. The most effective way to prevent large amounts of file fragmentation is simply to give the file system & OS plenty of free space to work with, which is a major reason not to unnecessarily divide the drive into smaller partitions.

I'm still somewhat amazed that so many users think they can do better on a single drive system than what Apple provides as the default. It is the result of years of research & highly optimized OS design efforts. Since it would be quite easy to build in these user devised schemes as defaults, at least ask yourself why Apple hasn't done that if they actually had any real advantages. Do you really think Apple somehow missed something that users have not?

Hi Verseau1955:

Now that we have confused you, I'll give you a more practical answer. Use a single partition, keep
it tip top shape using iDefrag. I am not recommending the defrag utility so much for its defrag
ability, but rather for its ability to optimize file placement on the hard drive. I use iDefrag
regularly on my system, and for quite some time now, I only use the optimize algorithm setting.

The optimize setting is exceptionally good on drives with single partitions because it moves system
files to the beginning of the drive for best performance. It also moves apps next to the system
files for best performance as well.

It is usually not necessary to run iDefrag until after software updates like the OS update (10.6.1 -
10.6.3). Snow Leopard is pretty good about maintaining a tidy system file layout.

The only setback to this setup is that you have no control over what part of the drive your
photoshop scratch files will reside on, especially once the drive starts filling up with data.

If you really want blazing performance, install a 300GB velociraptor drive and put that 700GB
drive in an external firewire case and use it to hold your completed data files, that way you
will always keep plenty of space available on the boot drive.

KJK555 wrote:
I am not recommending the defrag utility so much for its defrag
ability, but rather for its ability to optimize file placement on the hard drive.

OS X is quite capable of optimizing file placement without the need of a third party utility.

The optimize setting is exceptionally good on drives with single partitions because it moves system
files to the beginning of the drive for best performance. It also moves apps next to the system
files for best performance as well.

Again, this assumes incorrectly that system & application files are the only ones that should be located on the fastest part of the drive, ignoring the importance of frequently accessed user files, especially those in ~/Library/.

If you really want blazing performance, install a 300GB velociraptor drive and put that 700GB
drive in an external firewire case and use it to hold your completed data files, that way you
will always keep plenty of space available on the boot drive.

KJK555 seems to have lost sight of the fact that the O.P. has an iMac. iMacs do not offer easy access to the drive for replacement & some skill & special tools are required to open the case without damaging anything. Additionally, putting a 10,000 RPM drive optimized for high performance server use like the VelociRaptor into an iMac is probably not a good idea from a heat & noise standpoint. Depending on the iMac's vintage, it may not even be able to take advantage of the SATA 3 Gb/s interface of the VelociRaptor or work properly with it. In short, it is not an optimal drive for iMacs.

The most practical advice I can offer is simply to use Apple's default single partition configuration, let the OS handle file optimization, & use the iMac as intended as a maintenance-free computer that lets users concentrate on using it rather than wasting time doing dubious tweaks for mostly mythical performance improvements.

+"KJK555 seems to have lost sight of the fact that the O.P. has an iMac. iMacs do not offer easy access to the drive for replacement & some skill & special tools are required to open the case without damaging anything."+

True.

+"Additionally, putting a 10,000 RPM drive optimized for high performance server use like the VelociRaptor into an iMac is probably not a good idea from a heat & noise standpoint. Depending on the iMac's vintage, it may not even be able to take advantage of the SATA 3 Gb/s interface of the VelociRaptor or work properly with it. In short, it is not an optimal drive for iMacs"+

False.

I just checked the temperature of the 4 drives in my Drive Bay.
Bay1: 83℉ - WD1000
Bay2: 79℉ - VelociRaptor
Bay3: 85℉ - WD500
Bay4: 83℉ - WD500
VelociRaptor is a 2.5 inch drive and doesn't stir up as much heat as the 3.5 inch drives.
VelociRaptor is not as noisy as the WD500 it replaced.
VelociRaptor works fine on a Sata2 interface, which I believe the iMac uses a Sata2 interface as well.
VelociRaptor has a 5 year warranty, and you probably won't have to replace it for 5 years or more.

+"OS X is quite capable of optimizing file placement without the need of a third party utility."+

False.

It does nothing of the sort, except during installation or restoration of an OS backup (TM or DU).
If I leave my OS alone long enough (as little time as a month or two) it will have System and User
support files scattered from one end of the boot volume to the other and the bulk of my data isn't
even kept on the boot drive. Pics, videos and business files are kept on (symlinked) to another
volume. At present my User account is only 14.74 GB and 7.05GB of that is my Downloads folder,
in other words just the usual user and application and frequently accessed user support files are
kept on my boot drive.

Just for grins I opened iDefrag to check for fragmented files. Safari's cache.db user file was in 248
pieces (that's better than usual), some other various user and temp files were in 60 -100 pieces.
System files were pretty sane though, but as usual, OS X could care less about defragmenting
user files, even the ones less than 20MB.

+"Again, this assumes incorrectly that system & application files are the only ones that should be located on the fastest part of the drive, ignoring the importance of frequently accessed user files, especially those in ~/Library/."+

Excuse me for forgetting to mention the frequently accessed user files, iDefrag doesn't forget about
them though, and it places them in the right place.

KJK555 wrote:
I just checked the temperature of the 4 drives in my Drive Bay.
Bay1: 83℉ - WD1000
Bay2: 79℉ - VelociRaptor
Bay3: 85℉ - WD500
Bay4: 83℉ - WD500

What makes you think you can compare the cooling for two such radically different designs as an iMac & a Mac Pro?

If I leave my OS alone long enough (as little time as a month or two) it will have System and User
support files scattered from one end of the boot volume to the other and the bulk of my data isn't
even kept on the boot drive.

Do you suppose the two things are related? OS X only defragments the startup drive & applies hot file clustering to it, & prefers lots of free space to keep file fragmentation (multiple segments) from happening.

Just for grins I opened iDefrag to check for fragmented files. Safari's cache.db user file was in 248
pieces (that's better than usual), some other various user and temp files were in 60 -100 pieces.

Cache & temp files are constantly being written to. Of course they get fragmented but it is pointless to try to keep them defragmented -- you will spend far more time doing that than you will ever save from faster access.

System files were pretty sane though, but as usual, OS X could care less about defragmenting
user files, even the ones less than 20MB.

Funny, on all my Macs, which keep system & home folders on the same very large partitions, OS X controls user file fragmentation quite well -- I've never seen more than 1% total file fragmentation & it is usually much less.

I think you are just creating a situation where fragmentation is more likely to occur, so you do need iDefrag. Just use as large a startup partition as is feasible, use the defaults for storage locations & the OS does a great job … & it does it in the background with no loss of uptime.

+"What makes you think you can compare the cooling for two such radically different designs as an iMac & a Mac Pro?"+

Cool is Cool Baby!
The boot drive, which is by far the busiest drive at the moment, is running the coolest at only 7℉
above ambient temperature, but if you really want a cool running drive, get an SSD!

+"Do you suppose the two things are related? OS X only defragments the startup drive & applies hot file clustering to it, & prefers lots of free space to keep file fragmentation (multiple segments) from happening."+

I have plenty of free space on my boot drive.
I am using at the moment 55GB of space and I have 107GB free.
After I clear my desktop of video files, I will free another 17GB of free space.

+"Cache & temp files are constantly being written to. Of course they get fragmented but it is pointless to try to keep them defragmented -- you will spend far more time doing that than you will ever save from faster access."+

Safari's cache file gets fragmented so badly, Safari will start crashing. That's a known fact, and even
when safari is not being used, OS X won't defragment it. I guess that's why Safari has an "Empty
Cache" menu function, but when you empty it, you lose your history. Interestingly enough,
most other browser's caches won't become corrupt or fragmented like Safari's does.

Temp files I don't worry about. Mostly just pointing out that OS X doesn't defragment files that are
not system files, and that includes user account files. How much fragmentation happens is pretty
much proportional to the amount of changes a person makes to his user files. If you don't do
much, you don't fragment much.

+"Funny, on all my Macs, which keep system & home folders on the same very large partitions, OS X controls user file fragmentation quite well -- I've never seen more than 1% total file fragmentation & it is usually much less.+

+I think you are just creating a situation where fragmentation is more likely to occur, so you do need iDefrag. Just use as large a startup partition as is feasible, use the defaults for storage locations & the OS does a great job … & it does it in the background with no loss of uptime."+

I rarely see more than 1% actual file fragmentation either. OS X usually suffers more from free space
fragmentation than it does file fragmentation. Free space fragmentation can slow down file transfer
as much or more than simple file fragmentation in some cases.

Most of my volumes never need defragmenting. Then again, some do need an occasional defrag,
especially the ones that contain ever changing backups on SB image files.

No, I couldn't fit all my data on a single drive if I wanted to. It wouldn't all fit, not even on a 2TB
drive.

KJK555 wrote:
Cool is Cool Baby!

Don't be silly. Mac Pros have very heavy duty (& bulky!) cooling systems. iMacs do not.

Safari's cache file gets fragmented so badly, Safari will start crashing. That's a known fact …

Known to whom? Safari is rock stable on all my Macs.

I guess that's why Safari has an "Empty
Cache" menu function, but when you empty it, you lose your history.

Funny, doesn't happen on any Mac i've ever tried it on since Safari was released.

Free space fragmentation can slow down file transfer
as much or more than simple file fragmentation in some cases.

So wrong it isn't even worth arguing about.

"Just installed a Western Digital Velociraptor WD3000HLFS SATA drive into my white (2006) 24"
Core2Duo iMac w/2GB RAM. Others have commented that these drives are noiser, however my
experience has been quite the opposite with complete silence even under heavy disk loading.
(I think the iMac design should muffle most drive noise (compared to tower case designs). An
earlier VR/iMac owner didn't mention any drive noise. But there were some drive noise complaints
from pre-2008 Mac Pro owners IIRC (2008 Mac Pros have rubber isolators in the HD bays that
should help a bit) - Oliver used an HD isolator in his (1st gen) Mac Pro to address that. (ref: How I
"Silenced" a WD Raptor in a (1st gen) Mac Pro ).-Mike)
Boot time in Leopard 10.5.5 is greatly reduced, and the system is much 'snappier'.

Installation process was a little simpler than some of the walkthroughs that I've seen around the
web, as there was less of the 'foil' to be removed/replaced once inside. It took around 15 minutes
end to end, and gave me an opportunity to clean out some dust and get into the corners of the LCD
to clean it properly.
Just make sure that you have some rubber cement handy for the temperature sensor to be re-
applied to the drive.
-Scott"
http://www.xlr8yourmac.com/archives/nov08/110608.html

*+Rubber cement!?!+*

Safari 3.2.1 (#2): more crash fixes:
http://reviews.cnet.com/8301-13727_7-10329914-263.html

http://forums.macosxhints.com/archive/index.php/t-100546.html

empty the cache:
http://discussions.apple.com/thread.jspa?messageID=11469430&#11469430

You do understand that file fragmentation & file corruption are two different things, right?

Message was edited by: R C-R

"Condition 1 is referred to as file fragmentation, while Condition 2 is referred to as disk
fragmentation or, more precisely, free space fragmentation. File fragmentation causes
performance problems when reading files, while free space fragmentation causes performance
problems when creating and extending files."
http://www.diskeeper.com/fragbook/chapter2.htm

Free Space Consolidation Improves Operating System Performance:
http://findarticles.com/p/articles/mipwwi/is_20050229/aimark1970970106/

From iDefrag manual:

"Sensible arguments for occasional optimization of your disk include:

HFS+ is not very good at keeping free space contiguous, which can, in turn, lead to large files
becoming very fragmented, and can also cause problems for the virtual memory subsystem on
Mac OS X.

Older versions of the Mac OS are not themselves aware of the metadata zone policy, and may
disrupt its performance.

HFS+ uses B-Tree index files to hold information about the filesystem. If a large number of files
are placed on a disk, the filesystem may have to enlarge these B-Tree structures; however, there
is no built-in mechanism to shrink them again once the files are deleted, so the space taken up
by these files has been lost.

Whilst HFS+ is good at keeping individual files defragmented, mechanisms like Software Update
may result in files that are components of the same piece of software being scattered across the
disk, leading to increased start-up times, both for Mac OS X itself and for applications software.
This is a form of fragmentation that is typically overlooked.

Defragmenting disk images can be helpful, particularly if they are to be placed onto a CD/DVD, as
seeks on CD/DVD discs are particularly expensive.

Some specific usage patterns may cause fragmentation despite the features of HFS+ that are
designed to avoid it."
#

*Rubber Cement - Priceless* 🙂

+"You do understand that file fragmentation & file corruption are two different things, right?"+

Certainly, but in Safari's case the two are somehow related. Once the cache exceeds 300-350
fragments, that's when safari becomes unstable, and not before.

Why, I don't know, but that's what has been observed. Perhaps a buffer overflow or something.