Drive manufacturers do map out bad blocks before the drives are released from manufacturing. The bad block list created during this process is not the same as the disks Grown Defect list (G-List). The original bad block list is permanent and cannot be altered. The G-List can be changed by various utilities designed to write out new G-Lists to the drive.
When you format a hard drive, the permanent bad block list, and the G-List are used during the initialization process (actually some formatting tools give you control over using the G-List and or permanent bad block list or not, however for this discussion, the G-List is always used).
Using Apples Disk Utility, the only way to write out a new G-list is to use the Zero data option during formatting.
So if you do a default format, you will erase and format the drive using the permanent bad block list, and any existing G-List. If you use the Zero the data option, the format process does a media check by doing a write read of zero's to the media. When the media check is done, a new G-List is written out with any defects noted. The drive is then formated with the perement bad block list and the G-list.
Which brings us to an interesting question...
Since a brand new hard drive has already had the media checked and the permanent bad block list created.
The drive hasn't been used, except for testing at the manufacturer.
What value is there in zeroing data on a brand new hard drive?
Bad blocks will occur over time as the drive is used, do to media failure, but the drive hasn't been used, so there should be no new media failures. In other words, the permanent bad block list, and the G-List will be the same if you use the Zero data option on a drives initial formating.
Tom N.
