![]() |
The Disk Center |
||
Many factors can affect the performance and outcome of a backup task. One of the things that we have found particularly helpful for identifying performance problems, for example, is to have disk activity statistics available during a backup. CCC's Disk Center provides this kind of statistics monitoring, as well as general volume information for each locally-attached volume mounted on your Mac. Choose "Disk Center" from CCC's Window menu to view the Disk Center.

Basic volume information
The Disk Center window displays a list of locally-attached, mounted volumes in a table on the left. Click on one of these volumes to display information such as the volume name, filesystem, capacity, and disk usage. CCC displays a level indicator next to the disk usage figure. When disk usage exceeds 70% of the volume capacity, the level indicator will turn yellow to indicate that you may want to consider "cleaning house". If the disk usage exceeds 90% of the volume capacity, the level indicator will turn red. Especially on a volume that contains an installation of Mac OS X, we recommend that you try to maintain at least 10% of the volume as free space. When you start to consume that last 10%, fragmentation becomes a problem and general performance of Mac OS X begins to decline.
Drive Statistics
The Disk Center will update disk activity statistics on a one-second interval. Disk activity is collected by Mac OS X at the hardware interface, so data for multiple volumes residing on the same disk will be identical. The data read and write rate can give you a good indication of how fast Mac OS X is able to read and write data from and to your disk. You will likely notice that these values fluctuate wildly over the course of a backup task. This is quite normal, write performance will generally be lower when copying lots of small files and higher while copying a larger file. When lots of small files are being copied, there is a lot of seek activity occurring on your source and destination volumes. This seeking greatly reduces the overall throughput compared to the theoretical throughput of your disks.
If your backup task seems particularly slow, stop the task and see what the baseline disk activity is. For example, while running a performance test, I couldn't understand the absolutely dismal performance I was seeing. In the middle of the task I had launched Safari so I could download and test Growl on my test system, and I didn't think it would have a measurable affect on the task. I stopped the task and noticed a persistent 1.8MB/s level of write activity on my source volume in the Disk Center. After a brief investigation, I discovered that Safari was writing massive cache files to my home directory. After quitting Safari, my backup performance was back to normal.
Disk error statistics
CCC will report error-related statistics when they are present. You can tell at a glance that something is wrong with this disk:

Read and write latency is a cumulative measurement of the amount of time that the disk interface had to wait for a read or write operation to return data (in cases where the operation ultimately succeeded). Read and write retries indicates the number of times that the disk interface had to make multiple attempts to retrieve data (again, this value only pertains to attempts that were ultimately successful). Read and write errors indicate the number of read or write attempts that were simply unsuccessful. The meaning of each of these values is less important than their meaning as a whole. If you're seeing any red data in the Disk Center, there's a good chance that your hard drive is suffering a hardware problem.
Full Disk Encryption (Lion only)
Apple introduced a new "Full Disk Encryption" feature to Mac OS X Lion, and that functionality is exposed for Lion users in the Disk Center Encryption tab. CCC allows you to convert HFS+ formatted volumes that reside on a disk that is partitioned with the GPT partitioning scheme to CoreStorage encrypted volumes. You can also use the Disk Center to monitor the progress of the conversion process, and to disable encryption on a CoreStorage encrypted volume. Please note that CCC is exposing functionality provided by the OS, CCC is not actually engaged in the encryption process. As a result, you can manipulate CoreStorage encryption with CCC's Disk Center, then close the window, quit CCC, run backup tasks, etc. while the conversion is handled by the OS.

Some considerations before you enable CoreStorage encryption on a volume
Your data will only be accessible on Mac OS 10.7 Lion Once the volume is encrypted, you will not be able to read its contents on any other OS.
CoreStorage Encryption is a new feature Because Apple's Full Disk Encryption is a new feature and because the nature of the feature can have a significant impact on your ability to access data on an encrypted volume, we recommend that you limit the use of this functionality as Apple has: to the startup disk (via the Security Preference Pane) and to a backup volume (with CCC's Disk Center).
CoreStorage encryption is Apple-proprietary CCC's ability to manipulate CoreStorage volumes is limited to the functionality exposed through the diskutil command-line utility. If you encounter problems while enabling CoreStorage encryption on a volume, CCC will tell you everything that it knows, which is likely very little.
The encryption key storage object is opaque CCC cannot (legitimately) manipulate this object to accommodate differences between two volumes. As a result, the interface upon startup will be limited to a generic "Unlock the disk" password field. When you encrypt a startup disk in the Security Preference pane (e.g. rather than in CCC's Disk Center), you get the following advantages:
- You can store your master key on Apple's servers, which could come in handy if you forget or lose your passphrase
- Any user account can unlock the volume and start the computer
- You get an elegant loginwindow-like UI on startup for your backup volume
If any of these advantages appeals to you, you can create your bootable, encrypted backup with these steps instead of converting the backup volume with CCC's Disk Center:
- Install Lion onto your empty, unencrypted backup volume. This step is required to create the Recovery HD partition, there's more info on this below.
- Reboot from your production installation of Lion and clone Lion to your Lion backup. This will synchronize user accounts and your personal data onto the fresh installation.
- Boot into your Lion Backup and enable encryption in the Security preference pane (the Recovery HD partition is required for this step).
- Carry on with ordinary usage and backup hygiene while booted from your production installation of Lion.
The conversion process may take a couple days Converting a volume to a CoreStorage encrypted volume requires that each block on the volume gets individually encrypted. This process works quietly in the background (consuming a modest amount of CPU), and you can use the volume during the conversion process, but it will result in a constant din of disk activity for many hours.
Use Disk Utility instead if you can start from scratch If you can start with an empty volume, you should format the disk as CoreStorage encrypted in Disk Utility. Converting an empty volume to CoreStorage encrypted is, quite frankly, a waste of CPU cycles and energy. When you format the volume as CS Encrypted directly in Disk Utility, there is no conversion process, the disk is immediately encrypted. If you don't need to convert a backup volume, reformat it instead in Disk Utility.
Please don't make the decision to encrypt a volume casually. Give the preceding limitations careful consideration and understand that encrypting a startup disk outside of the Security preference pane is unlikely to be an Apple-supported configuration. We do not recommend enabling CoreStorage encryption on any volume other than a backup volume whose complete data set is retained on another volume.
Enable encryption on a volume
To enable CoreStorage encryption on a volume, click on the volume, then click on the "Enable encryption on (volume name)" button in the Encryption tab. CCC will prompt you to provide an encryption password for the volume, and offers the convenience of adding that password to your keychain. You will need this password to unlock the volume whenever it is attached to your Mac. CCC will store this passphrase in a private keychain so the volume can be mounted automatically during a scheduled backup task.
Disable encryption on a volume
Encryption can be disabled on any volume that is CoreStorage encrypted, and not currently in the process of converting to an encrypted volume. To disable CoreStorage encryption on a volume, click on the volume, then click on the "Disable encryption on (volume name)" button in the Encryption tab. CCC will prompt you to provide your encryption password for the volume, then will begin the process of converting the disk to an unencrypted volume. Note that the decryption process will also take a considerable amount of time, and cannot be cancelled. You can continue to use and access the volume during the decryption process, and you do not need to have CCC open for the process to continue.