>Whoa.
>You just hit one of my pet peeves, so apologies if I get a bit ranty... :)
>
> From now on, each time you have a disk problem and find yourself
>reaching for a defrag/optimization utility, please grab a bibble
>(Holy, Unholey, Mac, Unix, VMS, etc) and smack yourself on the
>forehead with it. Repeat as necessary.
>
>hum. Terminology: "Block" is a logical (software) term used to
>describe a collection of data. When speaking about disk drives, a
>block is usually 512 bytes. "Sector" is the physical (hardware) area
>on a disk platter that holds one block of data. Disk drives
>read/write one or more "clusters" (groups) of sectors at a time.
>Note that you can format a drive to have a different sector size.
>Bigger sectors are more efficient for holding bigger files, but the
>MacOS is really optimized for 512 byte sectors.
>
>Corruptions occur because of only two problems: bad blocks of data
>were intentionally written (spazzing software or bus problem) or a
>disk sector has degraded[*].
>
>[*] Sectors can sometimes degrade or die. Some drivers automagically
>map out those bad sectors and let you continue using the drive.
>That's normal and nothing to worry (much) about. When a drive
>suddenly looses a LOT of sectors, that's called a crash! The most
>frequent type is a "head crash", which occurs when one of the r/w
>heads goes the extra micron or so and actually scrapes a platter's
>surface - blowing off schrapnel. Kindof like a jet engine after it
>sucks in a frozen turkey (but that's another story). Not good.
>
>Ok, back to that defrag thing... Lifting every block of data off
>your disk drive, with a "defrag" utility, then dropping it onto a
>different sector is the LAST thing you ever want to do. This isn't
>"repairing" anything! This is taking the existing corruptions and
>just moving them around or even replicating them! If the corruption
>was due to a slightly degraded sector in a file's data then the next
>file that gets put onto that sector will also become corrupted! If
>the corruption was in the HFS/HFS+ indices, then you might end up
>loosing access to more files!!!!
>
>What you need to do is *repair* the volumes on the drive. That's
>done with Disk First Aid, Disk Warrior, Disk Doctor, etc. NOT with a
>defragger.
>
>
>Disk defragmenter/optimization programs were originally pushed for
>the PC market because the DOC/Winblows file system really sucks and
>tends to fragment files so badly that PCs grind to a halt. Yes, the
>MacOS' file system does fragment files, but not nearly so badly as
>Win AND it's designed to handle it properly!
>
>There are really only two times you *need* to use a defragger:
>
>1) Once a year or so, as a total system maintenance regimine.
>
>2) On a specific volume that you're using for a lot of audio/video
>capture work if your system and/or drives aren't fast enough to keep
>up with scatter/gather.
>
>Really, the best way to optimize a drive is to initialize it, then
>refill it from scratch from a full backup. That way you get a *new*
>*clean* file system built!
>
>FWIW, I dispise defraggers so much that I absolutely won't use them
>on my own or on my client's systems.
>
>- Dan.
I can't totally agree with Dan as my experience with defraggers
(TechToolPro and Norton) has been generally positive with good overall
response from maintenance applied every month or six weeks - but I think
my problems were special software related so the maintenance had a reason
rather than being a routine exercise. The software problem was a mix of
very large maths and programming apps which did not get along well
together and my mac would gradually slow down to a crawl - may well have
been all the extensions related to these apps but to make a special set
for each app and then a general set for normal use would have been a
thankless task as I had no real idea which extensions belonged to which -
Mathematica was especially prone to freezing and crashing with it's
strangely 'active' interface and Excel's AutoSave had problems with the
energy saver. To reinstall was major hassle as I had proxy ed licence for
some of the software like Matlab 5.1.3 as it was no longer available to
buy for mac and the install cd was two hundred miles away. I have
separate workstations now thankfully.
So it was because of the slowdown that I resorted to mirrored boots
with two identical boot volumes with the utilities on (too slow from a
boot cd) and a third volume with all the apps. I did regular
maintenance,directory rebuilds and defrags and system checks and it
worked very well and cured the slowdown for a year and a half but I
learned that this route is not to be taken lightly - backup must be done
before maintenance as the defrag does indeed lift and reposition most of
the data so I'm not recommending any procedures here - horses for courses
- I had a specific problem which it cured. During this period I had just
one nightmare when the defragger froze 95% of the way and I hadn't backed
up - complete shambles and a nauseating experience with imaging maths
software where every line of script can take hours to put together.
(The specific Neugebauer model I was building was based on a paper
by Pobboravsky and Pearson of RIT published by TAGA and the equations in
the paper contained a mistake - I eventually had to email THE Irving
Pobboravsky (now retired and I hope it lasts a long time) for a different
approach to the problem - I thought I'd mention him as he's a credit to
USA imaging research.
DiskWarrior - to my knowledge (which is not great but I have no
problem with being enlightened) - defrags the directory - an operation
also performed by TechTool.
DiskDoctor I have not had good fortune with - I ran it on a couple
of fast two gigs and somehow killed them both....
Pete
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