Hard disks *do* get slower with use

The question is why?We've been so conditioned to think that various evils - malware, fragmentation, bad blocks, and general bit rot, among others - are hosing our disk performance that we forget that hard disks really do get slower with use.

The question is why? We've been so conditioned to think that various evils - malware, fragmentation, bad blocks, and general bit rot, among others - are hosing our disk performance that we forget that hard disks really do get slower with use. It is natural and unavoidable, but there are some things you can do to mitigate the effects.

Remember how snappy your new computer seemed? It isn't just the new computer smell. Even if your machine never installed a single virus or fragmented a single file, your disk performance does decrease with use. Here's why.

Circles within circles within circles Data is laid on disks in blocks called sectors which contain your data and other info, such as EDC, to keep it safe and available. The sectors are laid down in circular tracks.

Disk engineers saw a long time ago that they could put more sectors on the outside of a disk platter than on the inside. Once disk microcontrollers got fast enough, it became possible to implement something called Zoned Bit Recording (ZBR) to take advantage of geometry.

Track star ZBR puts more sectors on outer tracks than inner tracks. Adjacent tracks are grouped in zones that all have the same number of sectors. As the zones move closer to the center of the disk, they have fewer sectors.

As bit densities increase, more sectors can fit on a track, and more tracks can fit on a disk. Over time, disks have also added more zones: 10 or so in the '90s; 30 or more today.

ZBR giveth and ZBR taketh away The outermost track on a disk has the fastest data rate. The outermost track is also the first place that gets loaded on the disk. So the most valuable disk real estate gets occupied first. As more stuff gets added, you are moving from Boardwalk and Park Place down to Baltic and Mediterranean, i.e. the low-rent district. As you use more disk capacity, the disk gets slower.

The slowdown varies by disk model, but figure the innermost zone is half the data rate of the outermost. Not a big deal for small files, but putting the latest version of Office on a nearly full disk ensures you'll have a lifetime of slow Office booting.

Ashes to ashes, bits to bits There is practical use for this info.

  • On a new machine, delete all the demo-ware before installing applications you do use.
  • Likewise, delete all the capacity hogging applications that you'll use only occasionally, install the big apps you do use, and then re-install the capacity hogs you'll rarely use.
  • If you are an active consumer of new applications it could be worthwhile to backup your disk, zero it out, and then reinstall the OS and your new favorite apps and then everything else.

I have no idea how you'd do this on Windows - reader suggestions welcomed The idea is the same for either OS.

On a Mac it is pretty easy (newbies, you should leave the room now). First, using something like the free Carbon Copy Cloner or Super Duper, create a bootable backup on an external drive. Then, using the free Omni DiskSweeper, figure out which are your largest applications - not forgetting the Application Support folder in the Library. Make a list.

Reboot using the external drive. Using Disk Utility, zero out your internal drive. Do a custom install of OS X, leaving out the three GB of printer drivers and the hundreds of megabytes of foreign language support.

Next, unless you use them often, don't install iLife or the iWork 30 day demo package, which total about 7.5 GB, including the Garage Band instruments and the iLife audio loops. There, you've just saved 11 GB of your highest performance disk capacity for more important - to you - stuff.

Now, install the big important apps you do use, such as Office or Halo. Then the less used large apps and so on, which might include iLife and iWork. Save iTunes for last, since audio files don't need much in the way of performance.

Over time as your disk fills it will still slow down. But your carefully installed important apps will continue to load as fast as they can.

Comments welcome, of course. And smart Windows guys: how would you do the equivalent?


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