Microsoft Word Hardware Reconfiguration Methodology V final2

Data file volatility

A determining factor for selecting the appropriate type of backup scheme will depend on whether the files to be backed up contain volatile state-based information about the operating system or some arbitrary application or service. Consider the following:

1. 
   Operating system files that contain volatile data from directories such as /dev and /proc should only be backed up using Dump. Many of these files, especially from /proc contain very volatile system and application data (i.e. RAM, system and application states, etc.) and must be treated carefully.
   

2. 
   Some of the files are application and service-based and can be safely backed up when the offending application or service is disabled. Nevertheless, Dump can normally handle these files, even if they are left running.
   

3. 
   Device files (/dev), however, sometimes can be problematic. For device files that must be backed up but that cannot be accessed, disabling a specific device will often work. Dump can normally backup these files even if they are in use. However, in case where they cannot be backed up Dump, DD can be used, but only if the filesystem is quiescent.
   

4. 
   If for some reason certain files that must be backed up cannot be accessed regardless of what is attempted, then the system must be placed offline and backed up using a rescue or Live CD.
   

7. Running applications and services

A determining factor for selecting the appropriate type of backup scheme will depend on whether application-based files can be backed up while the application is left running. For example, it is generally not advisable to backup a database file while its corresponding application is running; buffered data may not have yet been written out to the database, potentially resulting in data loss upon restoration. Consider the following:

1. 
   An application of service left running can normally be backed up as is. Tar and Cpio are well suited for application-based backups. Dump can also be used although it is more of an all-purpose tool.
   

2. 
   If the application is a database application, then the application and its files can normally be backed up. However, database files should never be backed up while their corresponding applications are running.
   

3. 
   Many small database files can be backed up while their corresponding applications are running. This however, will however, depend on the type and size of the database. Larger databases and should always be shut down prior to backing up. This is due unwritten buffered data in memory. For smaller databases, unwritten buffered data may result in nothing more than several minutes’ worth of data loss. Larger databases, however, may be inconsistent and be rendered unusable if buffered data is left unsynchronized.
   

4. 
   Is the application data stored on partitioned or raw devices? Tar, Cpio, and Dump will on partitioned devices where a valid filesystem structure exists. DD is best suited to raw devices.
   

5. 
   Are the applications services? They too can normally be backed up. However, services often write data out to log files and these log files may not have been recently synchronized such that when backed up may not contain unwritten buffered data, resulting in partial data loss. If a service’s log file(s) is important then the corresponding service should be shutdown prior to backing it up. Normally, however, backing up services and their various files is not an issue.
   

6. 
   Are user data files currently in use by applications? Normally, user data files (i.e. word processing, spreadsheets, etc.) that are in use can be backed up. However, much will depend on file sizes and how often buffered data is synchronized. Normally, this will not result in corrupted files but may result in partial data loss. Therefore, in use user files can be backed up.
   

7. 
   If certain files are locked and the corresponding application or service cannot be shutdown, then certain files may have to be skipped. If the filesystem is active then DD can be used to acquire an image or the system can be taken offline and backed up from a rescue or Live CD.
   

8. 
   Are files being shared over the network? These files can also be backed up. However, if they are in are being edited or modified then what is in memory may not be consistent with what was backed up unless unwritten buffered data are synchronized out to disk before backing them up.
   

In summary, it should be considered a good practice to shut down all non-essential user- applications and databases before backing them up. If they must be left running, ensure wherever possible that unwritten buffered writes are synchronized to disk.

8.