If you've been running SBS 2003, and you've been a good administrator and you've been running backups, you've probably seen the backup error of dread!
Error returned while creating the volume shadow copy:800423f2
Reverting to non-shadow copy backup mode.
This error has good news and bad news. The good news is, before we shipped (like in the beta), this happened about 90% of all backups, now it happens about 0.01% of all backups. The bad news is, it happens on occation
So what is this error? Well, if you remember in my previous post I talked about VSS and how it works, primarily for snap-shots. I didn't mention what happens when you do a backup. Like I mentioned, doing a snap-shot for a backup is very much the same as doing a snap-shot for a previous version. But here is the difference.
In a snap-shot for a backup, the VSS service will call all the writers on the system. You can see how many writers you have on your system by opening up a command prompt and typing vssadmin list writers. Each application you install on your system should have a writer to work best with the backup.
First, What's a Writer?
A writer is built by the application for the application, it knows what to backup, and how to prepare the application for the VSS snap-shot. Of course, NTBackup doesn't use the first peice of information.
So how does the whole process work? Well, bkprunner is kicked off and launches NTBackup. NTBackup then tells VSS to do a snap-shot.
In order to get a backup where there are no open files, a snap-shot takes place, but for the backup, we want to make sure that all the data from all applications is no longer kept in memory, but rather is flushed to the disk. In order to do this, VSS performs these steps:
- Request Writers to Prepare for Backup - there is 1 minute alloted here for applications to write all their data to disk they want to have backed up
- Request Writers Freeze Applications - At this point, the Writers instruct their own application to hold all disk writes in memory. From this step, to the 6th step in this list, there is a hard stop at 60 seconds
- Request Filesystem Writer to freeze filesystem - This is when the file system is frozen and this writer will hold all writes to the disk from any application that doesn't have a Writer. From this step to the 5th step, is allotted only 10 seconds
- Take a snap-shot - This is where the actual snap-shot differential area is created an ready to accept new changes
- Thaw (or un-freeze) the filesystem - Write everything to disk that was held off before and allow more writes to the disk
- Thaw the applications - Allow the applications to start writing to the disk again
Well, the error 800423f2 happens when the system doesn't get through the above steps in the alotted time period. There are some handy tips and tricks on how to resolve this issue. The are located in the Backup Tips & Tricks section. Essentially, they boil down to:
- Make sure you have enough disk space on your disks, the system needs some to play with during a snap-shot
- The disk is not fragmented, there is a lot of disk activity during the start of a backup, if the disk is too slow, it can cause issues
- The Event Log isn't set too big. Due to the architecture of the eventlog and the it's writer, when a backup starts, the event log is paged from disk into memory, and then flushed out to disk again, which is pretty disk intensive
- Directory Auditing is disabled. Due to the nature of SBS being a single box all of the directory service authentication goes through this box. In the case of the backup, a lot of things are happening, and with directory auditing enabled, the box is just too busy to do the backup and all of auditing
There are some hotfixes out to making VSS work a little better:
KB 833167 - A Volume Shadow Copy Service (VSS) update package is available for Windows Server 2003
Now you know how it works, and knowning is half the battle!