Tip: Considering Disk Failures when Backing Up
In Leopard, Apple's Time Machine has been a welcome home-backup tool that many have adopted and use regularly. Its ability to restore the whole computer to within an hour's worth of work makes it ideal for accessing previous versions of work, or restoring
There are a variety of ways users can back up their computers, with multiple shareware and freeware archiving solutions, as well as full blown commercial packages that scale up for huge enterprise networks. In Leopard, Apple's Time Machine has been a welcome home-backup tool that many have adopted and use regularly. Its ability to restore the whole computer to within an hour's worth of work makes it ideal for accessing previous versions of work, or restoring recently lost files.
This backup system works great for most users, however it does not allow for a quick restore in the event of a drive failure. If the boot drive fails, users will have to order a new drive, wait for it to arrive, install it, and then restore the Time Machine or other backup to it in order to be up and running again. This can sometimes take days or weeks.
As such, it is recommended that users also consider keeping a regular cloned backup of their boot drive in addition to using Time Machine. In the event of a hardware failure, users can immediately boot off the cloned drive, restore the files they're working on to it from the Time Machine backup, and be up and running again in a matter of minutes. The popular cloning utilities SuperDuper and Carbon Copy Cloner both have support for scheduling, allowing users to keep at least daily clones of the boot drive.
NOTE: Cloning is not the same as Time Machine. Cloning will make a mirror copy of the boot drive, whereas Time Machine will retain previous versions of files in "snapshots" of the whole drive. Cloned drives are bootable, and Time Machine is not.
There are a couple of recommended setup for users to consider when combining Time Machine with a cloning routine:
1. Clone to a dedicated drive. If users have a separate external drive, periodically cloning the boot drive to it will allow users to boot off of it in the event of a failure by holding down the options key at system startup, and then select it as the boot drive in the "Startup Disk" system preferences.
2. Partition the Time Machine drive. Another option is to partition the Time Machine drive such that one partition is the same size as the boot drive, and then clone to that partition, using the rest of the space for Time Machine. This may only be preferred if the Time Machine drive is large enough to accommodate both partitions (ie: if the drive is at least double the size of the boot drive).
In both of these setups, the preferred route would be to clone to the fastest connection possible. For instance, having the clone on an internal drive is preferred to an eSATA connection (through a third-party card), which is preferred to a FireWire connection, which is preferred to a USB drive. One example would be a user with a 400GB boot drive an a 1TB FireWire "Backup" drive. Partitioning the backup drive to 400GB for the clone and 600GB for the TM backup is ideal. The ideal setup would depend on the user's specific situation, though in most cases any locally attached drive should work at the very least for either cloning or Time Machine.
Restoring: If users experience a boot drive failure and end up working on their cloned drive, restoring to a new boot drive is as easy as installing the drive and cloning directly to it again. There is no need to boot off installation DVDs and go through any setup. The drive just needs to be recognized the restore process started with the cloning program.
TM Exclusions: Since the system and support files are on the clone, users will not need to have them on the Time Machine backup, and as such users can add the "System" and "Library" folders to the Time Machine exclude list (in the Time Machine system preferences). This will allow for more room on the TM drive to back up data.
Other Options: While using a clone is the recommended choice for protecting against disk failures, another option is to set up a series of disks in a mirrored RAID array. This allows for one disk to take over immediately in case the main one is not accessible. Unfortunately, while RAID offers a more seamless recovery, the two types of mirrored RAID solutions (hardware-based and software-based) have drawbacks as well. For hardware RAIDs, in the event of a failure the bad drive can be immediately swapped out and the RAID will rebuild the mirror. This, however, requires a dedicated hardware controller and Macintosh computers do not come with one. Users will have to purchase a controller, which can be expensive. The software RAID, while supported in OS X, cannot easily rebuild the RAID. In the event of a hardware failure users will have to boot off the leopard DVD and use many command line tricks to get the RAID rebuilt on a new drive.
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