Time Machine wants to back up more then there really is?

[orbitalpunk]

hi there,

I asked TM to back up disk 2 to disk 3 and it said the backup is too large for the back up volume. its saying the backup is 466GB and the 465 is available only. these are both 500GB seagate drives and when i right click on finder to get info and disk 2, its only using 360GB. i did exclude invisible files and i did repartition disk 3. why is it wanting to back up more then there really is?

thanks

 

[Currawong]

Because a 500Gb hard drive isn't 500Gb, it's 465Gb. The "500Gb" is measured at 1000mb/GB instead of 1024mb/GB.

Also because Time Machine needs enough space to be able to make hourly backups. I imagine that some extra space is required for this. How they calculate it I don't know.

 

[orbitalpunk]

when i added each folder under excluded it works and calculates fine. but if i just add the whole drive i get that error. so it must be a bug. see if the calculated lated size of a drive is the same as counting each folder yourself is the same. i dont think it will be.

 

[/dev/toaster]

Sounds to me like your drive is too small. I am using a 500GB drive for 2 laptops with only 120GB drives. 500GB is barely enough for a month worth of snapshots.

 

[orbitalpunk]

why would it be too small? disk 2 and disk 3 are identical 500gb segate drives. if files can fit on one, why cant if fit on the other?

 

[jbardi]

why would it be too small? disk 2 and disk 3 are identical 500gb segate drives. if files can fit on one, why cant if fit on the other?

You are completely missing what is being said. Lets put it in basic terms and say this... if you want to use Time Machine correctly, don't backup to a drive that is the same size as the drive you want to back up. If you want to backup a 160GB drive, use between a 250GB - 500GB drive as the backup drive... if you want to backup a 500GB drive, you should be using between 750GB - 1 Terabyte drive as the backup drive.

Time Machine needs more space than the size of the drive because it is doing hourly, daily and weekly backups so that you can go back to many different days in the past to recover different copies of the same file. So you will not just have a single copy of one file, but a copy of that file plus data about all the changes to that file on each hour, day, week, etc, so it can recover that file from any point in the past that it was edited. Make sense?

If you just want a straight backup of your drive, then use SuperDuper or some other software that does a one-to-one image backup and then you can place that image on your other 500GB drive as it will be identical in size... as I stated in a different thread... use the right tool for the right job instead of complaining about why a screwdriver does not work well as a hammer.

 

[orbitalpunk]

i have superduper. but i liked the idea of incremental backups in TM. i see what your saying. but your not seeing what im saying. as i stated in my second post, if i pick the folders one by one, it calculates fine. can you explain that in your simple terms. read the entire post next time.