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I want to defragment my hard drive |
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A welcome side-effect of cloning one volume to another is that the files on the resulting volume are completely defragmented. While fragmentation is not as significant of an issue as it used to be (e.g. in the Mac OS 9 days), people that have begun to fill the last 10-15% of their boot volume may see some performance benefit from defragmentation. If you find yourself in this situation, this is also a really good time to consider migrating to a larger hard drive altogether.
Defragmentation is a natural result of backing up your data to an empty backup volume. Simply prepare your backup volume for use with Carbon Copy Cloner, then use either the "Backup everything" or the "Incremental backup of selected items" cloning method to back up your data. Note that you may need to leave the "Delete items from the target that do not exist on the source" option unchecked to avoid a block-level clone, which would actually preserve fragmentation.
"Clone, wipe, restore" — think twice before you wipe that original volume
It may be really tempting to do the following:
- Clone your boot volume — the one with your lifetime of irreplaceable data — to another hard drive
- Boot your Mac from that cloned volume
- Use Disk Utility to wipe the original volume
- Restore the cloned volume to the original volume
Very quickly you'll be booted back up from your boot volume and you'll have a backup to boot, right? In most cases, this would work out great for you, and you'd be fine. There are two really good reasons, however, to stop after the second step and take a breather:
- As soon as you erase the original volume, you're down to one copy of your data — you have no backup. The restore task will stress both the source and target disks with massive reads and writes. If either disk were on the verge of failure, this level of stress could push it over.
- You really should take the time to verify your backup. I trust CCC with my data, but do I trust that I asked it to copy the right items? Did my source volume have some crazy filesystem error that went unnoticed?
The Best Practice for defragmenting your hard drive
- Establish a backup regimen to a primary backup volume. Test your backups regularly.
- Quit open applications and use CCC to update your backup one last time.
- Use CCC to clone your hard drive to some physical volume other than your primary backup.
- Boot from the cloned volume.
- Use Disk Utility to reformat your original volume.
- Use CCC to restore your cloned volume back to the original volume.
- Boot from the original volume.
Performance upon first boot from a cloned volume will always be slightly slower than normal as Mac OS X reindexes your data and reestablishes hot-file clustering. When the system has "settled down", you will be able to evaluate whether the defragmentation has offered any performance benefit.