Time capsule backup failure after moving and changing internet access

Question

I bought a 1GB time capsule to backup my MacBook Pro using time machine and also archived files so I would have these when I had to move across country to work temporarily. The time capsule was working fine in my home after the original backup through an ATT DSL, but I then moved across country and set up a Comcast cable DSL and now Time machine records under Backing up: Preparing and the latest backup records failure. Is there a way of fixing this without erasing the entire Time Capsule and then taking 2-3 days of backing up again and will I have access to these when I return to my original home with the capsule and MacBook Pro. I have tried resetting all the backup modes and options.

Answer 1

Linda,
According to the logs, you are going to need to initiate a backup, and then let it do it's thing uninterrupted, perhaps all day of over night. Time Machine needs to do a "deep traversal". See this article.
*_Time Machine May Report "Preparing..." For a Long Time_*
First, it’s good to determine WHY Time Machine is "Preparing..." for an extended period of time. Examining the Console logs during this event can reveal what is actually going on behind the scenes. It may be “Preparing…” for a genuinely good reason. How long is 'too long' to wait for Time Machine to finish "Preparing..."? Some times, "Preparing..." is required to perform the normal housekeeping that Time Machine does periodically. Other times, it really is "stuck" and never proceeds after many hours.
*”Deep Traversal” (Recent Crash / Forced Restart / System Update / Extended Period Between Backups)*
According to the following KB article it can sometimes take quite a long time if Time Machine begins a “deep traversal” and has to compare data inventories. This may apply to your situation, particularly if many Gigs of data are involved. [http://support.apple.com/kb/TS1516]
You see, Time Machine *+does not+* ordinarily perform file-by-file comparisons to determine what has changed and thus determine what needs to be backed up. Rather, Time Machine relies on FSEvents notifications. This is a log that the system uses to keep track of changes to directories. Rather than scan tens of thousands of files for changes each time, Time Machine simply looks at this log and narrows its’ scan to only the directories that have experienced changes since the last backup. Otherwise, Time Machine would have to be running constantly just to catch every change on its own and thus eat up precious CPU.
Every event that FSEvents records has its’ own ID which includes a time stamp. At the end of every backup, Time Machine stores the last event ID that it processes. When the next backup is initiated, Time Machine looks at this stored ID and determines that it only needs to backup events that have occurred after the time stamp on this last event ID.
If, due to a system crash, power failure, forced restart, or some other major system event, Time Machine cannot find this last event ID in the system logs then it will consider the FSEvents log “untrustable” and it will go into what’s called “deep traversal”. The Console logs may report +“Event store UUIDs don't match”.+ In this event, Time Machine will by-pass the system log entirely and perform its’ own file-by-file comparison to determine what has changed since its’ last backup. Obviously, if tens or hundreds of Gigs are involved, then this process can take quite some time and should be allowed to proceed.
Additionally, it appears that if Time Machine has to go back too far to find the last event ID, then it will give up and simply go into “deep traversal” and do the file-by-file scan on its’ own. This can occur if Time Machine has not been able to perform its’ hourly backups for some time, as is the case for users who only backup once a week or so. This is also the case with major Mac OS system updates that change thousands of files at one time. There are simply too many events logged by the system for Time Machine to bother looking for the last known event ID.
Cheers!