Backup Algorithm
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What's the strategy of backup programs when files are in use? If you back up a file during use, your backup may end up useless because of inconsistent data. So, should a backup program should attempt exclusive access on every file it backs up? And if it can't gain exclusive access, maybe come back to that file later?
The difficult we do right away... ...the impossible takes slightly longer.
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What's the strategy of backup programs when files are in use? If you back up a file during use, your backup may end up useless because of inconsistent data. So, should a backup program should attempt exclusive access on every file it backs up? And if it can't gain exclusive access, maybe come back to that file later?
The difficult we do right away... ...the impossible takes slightly longer.
-
What's the strategy of backup programs when files are in use? If you back up a file during use, your backup may end up useless because of inconsistent data. So, should a backup program should attempt exclusive access on every file it backs up? And if it can't gain exclusive access, maybe come back to that file later?
The difficult we do right away... ...the impossible takes slightly longer.
As you have pointed-out; a backup of files alone is not enough to guarantee synchronisation on restore. Even if all files can be accessed there is still the time-sync/event-sync problem. A backup from which an app can restore itself is usually called a checkpoint. Such a "backup" would involve a transaction history file and a log file, as well as a "checkpoint" copy of pertinent files. Such backups are always built-into the app itself. The restore phase restores the files and then runs the app forward using the transaction history elements as input. The app must be suspended for the time it takes to perform the checpoint. There are techniques for minimising the timespan of the suspension, such as file twinning. A system-wide backup is not in my ken for today's platforms. However, anti-malware apps perform system-wide scans all the time, so I don't think file access is an issue, here. So what kind of backup do you have in mind?
Tadeusz Westawic Sumi quid sum.
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As you have pointed-out; a backup of files alone is not enough to guarantee synchronisation on restore. Even if all files can be accessed there is still the time-sync/event-sync problem. A backup from which an app can restore itself is usually called a checkpoint. Such a "backup" would involve a transaction history file and a log file, as well as a "checkpoint" copy of pertinent files. Such backups are always built-into the app itself. The restore phase restores the files and then runs the app forward using the transaction history elements as input. The app must be suspended for the time it takes to perform the checpoint. There are techniques for minimising the timespan of the suspension, such as file twinning. A system-wide backup is not in my ken for today's platforms. However, anti-malware apps perform system-wide scans all the time, so I don't think file access is an issue, here. So what kind of backup do you have in mind?
Tadeusz Westawic Sumi quid sum.
I want to perform a standard type of file backup where the files are compressed and encrypted into a single backup file. I think I'll simply keep a log file of which files I couldn't open for exclusive access, and leave it to the user to close whatever application is using the file.
The difficult we do right away... ...the impossible takes slightly longer.
