Solved: Archive Bit vs. Modified Date - what is difference...

Cletus9000 · ‎10-01-2015

I found this article:

https://www-secure.symantec.com/connect/forums/what-bettrer-archive-bit-or-modified-date-backups

but was wondering if there was anything else to it.

I notice that there is no longer a "copy" function (or i missed it). You used to be able to do a full backup "copy" mode where it ignored the archive bit - the "copy" backup backed everything up regardless of bit, it ignored it on backing up, and it didnt flip it once the file was copied. I don't see that option anymore.

Is there any difference between the two methods, other than described in that linked article?

I'm inclined to continue using the archive bit as the one sentence from the link has me a little squeamish about using "Modified Date":

"In case of files which are renamed, copied or whose attributes are changed, currently, you need to add these files manually in the backup job."

maybe the archive bit ALSO isn't flipped for these procedures, but i think i'll still just use the archive bit.

any thoughts or opinions?

pkh · ‎10-02-2015

I think this is just a cautionary note. Although the modified time of the file is not changed, they are captured in the incremental backup. You can test this by

1) creating two directories with a couple of small files

2) run a full backup to backup these directories

3) rename some files and copy some files between the two directories

4) run an incremental backup to backup these directories.

5) check the incremental backup set. You will find that all the copied and renamed files are in the incremental backup set.

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pkh · ‎10-01-2015

You should read the detailed description of these methods in the Admin Guide. There is no mention of the phrase that you referenced. For the newer versions of BE, modified time is the default method because it is faster and is applicable to most situations

Colin_Weaver · ‎10-02-2015

The archive bit process has to read the attributes of every file to decide what to backup in an incremental job. The modified time process will use a change journal that can be used to lookup exactly what needs to be backed up without having to access every file. So unless something has affected the change journal should be quicker.

Now with regards changes to metadata of the files I suspect there are possible ways to modify a file without either the archive bit or the mdified time/change journal records being updated, however, changing such attributes are not really part of the day to day operations against files and should be rare.

Something as simple as a file rename does reset the archive bit but appears to not reset the modified time (not sure what it does ot the change journal) This would however get reset if the end user also edited the file and the change would get caught on the next full (and we do not recommend incremental forever scenarios with Backup Exec)

Also I think a One-Time backup is deliberately designed to not interrupt a full and incremental sequence so works as a Copy backup used to - of course being one time it is there just for the odd emergency operation and not something you can set a repeat schedule against.

Cletus9000 · ‎10-02-2015

from this support article:

https://support.symantec.com/en_US/article.HOWTO99539.html

"A file's last modified date and timestamp do not change when the file is copied or moved. To ensure that the files are protected, run a full backup after you copy or move files."

Since we have users moving and/or renaming files all the time, i think the modified time would be a weaker solution than using the archive bit, even if the archive bit is a slower process.

Cletus9000 · ‎10-02-2015

great info Colin, thanks!

after seeing this article (as linked above as well), i think i'll stick with the archive bit even if it's a slower process.