At 09:39 PM -0800 02/06/2003, Terry Graham wrote: >Dan C wrote: > >At that point, the disk is usually repairable if you use Disk First >>Aid or another such tool on it. But the longer you wait (the more >>writing you do) the worse the problem gets... > >I've always run TechTool's defrag and Directory Maintenance at the slightest >sign of trouble because I've assumed that system and program >troubles compound themselves and by what you've explained, it makes >even more sense to nip >things in the byte. Thanks for this; it's a keeper.
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. (crawling back under my rock now) -- PCI-PowerMacs is sponsored by <http://lowendmac.com/> and... Small Dog Electronics http://www.smalldog.com | Refurbished Drives | -- Sonnet & PowerLogix Upgrades - start at $169 | & CDRWs on Sale! | Support Low End Mac <http://lowendmac.com/lists/support.html> PCI-PowerMacs list info: <http://lowendmac.com/lists/pci-powermacs.shtml> --> AOL users, remove "mailto:"; Send list messages to: <mailto:[EMAIL PROTECTED]> To unsubscribe, email: <mailto:[EMAIL PROTECTED]> For digest mode, email: <mailto:[EMAIL PROTECTED]> Subscription questions: <mailto:[EMAIL PROTECTED]> Archive:<http://www.mail-archive.com/pci-powermacs%40mail.maclaunch.com/> Using a Mac? Free email & more at Applelinks! http://www.applelinks.com
