TeraByte Unlimited

I was reading the backup strategies section of the manual and wanted to see if I could clarify something about sector-based backups.

Are there any situations where a file is "touched" by an app in such a way that only a couple sectors consumed by the file have changed, thereby making the differential process a snap, or is it a rule of the file system that anytime you see a new date on a file (as a result of its related program)--no matter how insignificant the changes are from the user's perspective--that all sectors comprised by the file were rewritten and a differential needs to sweep up all of those sectors?

I started thinking about this when it comes to PST (Outlook) archive files, which are often huge. Just opening one--not even changing anything in it--changes the date on the file.

Does whether a few or all file sectors change come down to how the app does things (efficiently or not) or is it driven by the the file system (NTFS)?

Only the changed sectors would be backed up.

Right, but what I'm trying to get at is whether it's routine or not for all sectors to be updated in file writes.

Depends on how the writing is done by the program. Both ways are common, but larger files are generally not completely rewritten. Database files, for example, are usually written out in records or even fields so updates only affect a small portion. Changing a line at the beginning of a text file will often require rewriting the entire file, while adding to the end doesn't.

OK, thanks. In the case of Outlook (which uses database-like files, I think), if I had to guess then, it's not rewriting the entire file. Traditional HDs are fast these days, but they're not so fast that writing out a file that size wouldn't be noticeable.

On Sat, 19 Jul 2014 21:44:47 PDT, just as I was about to take a herb,
rseiler disturbed my reverie and wrote:

> In the case of Outlook (which uses database-like files, I think), if I had to guess then, it's not rewriting the entire file.
I don't know if Outlook compacts the database files automatically at
all, but I do it manually every so often.
--
Cheers,

DrT

** You've never known happiness until you're married;
** but by then it is too late.