Does partitioning my disk erase my current data?

Repartitioning a disk will effectively erase all of the data on it. In truth, the data could be recovered by forensic means, but not through normal operation. What is happening is that you are defining for the system a new new structure for the storage. The old files are there, but the references to them are lost, so the operating system will not recognize the data is there (and will ultimately overwrite them).

Partitioning a disk takes a second. Formatting the partitions takes a few seconds if you do it normally. You have the option of securely wiping the disk by writing 0's or random data over whatever's already stored on the disk. That process takes quite a bit longer (because it has to write to every sector on the disk), and the exact amount of time depends on which secure erase level you select, the model of disk, and the amount of space.

I've never thought to time the procedure, but I believe [the internal iMac drives have a maximum sustained transfer rate around 78 MB/s|http://www.seagate.com/ww/v/index.jsp?vgnextoid=b9df99f4fa74c010VgnVCM1000 00dd04090aRCRD|pretty sure this is the drive used in my iMac]. At that rate it would take about 900 second (15 minutes) to zero out a 70G disk - though I would guess the utility zeroing it would incur a little overhead, so add a few minutes on top of that. If you used the 3-pass overwrite erase, that would take more than 3-times as long (3 passes, plus it has to generate a slew of random numbers). If you use the 7-pass erase, it would take 7x as long (plus some more since it has to generate all those random numbers).

More or less. The data will still be there (save for what's overwritten with the new partition headers), but you will have overwritten the directory structure so the names and locations of the files will have been lost and they'll be subsequently overwritten as you write data to the drive.

A person who is knowledgeable about such things could retrieve some data from the drive with special software. For example, law enforcement could extract files from the drive.

In short: if you want to retain your data, don't repartition the disk. If you want to wipe out your data, use the secure erase feature to make sure every last bit is gone.

In General reformatting or partitioning your drive will erase all of the contents on the drive. Though there is a way in Disk Utility that you can add a partition to an existing volume without affecting the original partition except for taking away a portion of the free space. However personally I would not try this unless I have all of my data backed up before hand just to be safe.

http://ftp.georgetek.com/George/Partition_1.png
http://ftp.georgetek.com/George/Partition_2.png
http://ftp.georgetek.com/George/Partition_3.png

George

That's correct and it works as I have done it successfully. However like I said I personally would not make any changes to my drive partition unless I had my files backed up.

George

Your drive is already partitioned. It has a single partition. Changing the number from 1 partition to a number greater than 1 would be repartitioning.

Partitioning a drive simply means writing out a table that specifies how the space is allocated on the drive. There's always partition information, even if there's simply one giant partition.

Regardless, the preceding posts still hold true.