One of the very best tools we have today to ensure both the longevity of our new hard drives and the reliability of those drives is to zero them out before putting them to use. MacGurus advises that every drive be zeroed before use to be certain of the quality and performance.
The process of writing zeroes over the entire surface of the drive not only tests the drive completely, to be certain of its quality from one end to the other, block by block , but makes the drive faster by burning them in. Comparing the amount of time each drive takes to complete the zeroing process gives us a great confidence as to whether each is fully and equally capable. All else being equal, good drives will take almost exactly the same amount of time to write a full pass of zeroes. Other processes being run simultaneously may effect the times, so care must be taken what else the computer is used for during the zero out process.
Today's hard drives are capable of doing their own housekeeping during operation. This means they can repair bad blocks all by themselves. To accomplish this they will go offline, make the repairs, and return to service, all autonomously and outside of our control. This process can take 30 seconds, 40 seconds or even over a minute to accomplish - an eternity in computer time. Writing a pass of zeroes over the entire drive forces this process to completion before ever using the drive for time sensitive data. This is critical for streaming media like audio or video drives since any interruption will cause dropped frames or a stutter.
Pretesting Drives for RAID
Zeroing your drives is especially important before putting the drives into a RAID array where each and every component drive plays a part in the overall performance and reliability of the array. In the event of any performance problems in a RAID array it is nearly impossible to determine which drive is causing a problem when all them are working as a group. Determination of a particular drive issue cannot be accomplished without breaking the array down and testing each component separately. By prequalifying your drives before building the RAID your results will have a better chance of meeting expectations. And in the event of a performance problem - breaking the array down and testing each individual drive by zeroing it out is probably the best possible test.
How to Zero on a Mac
Apple kindly gave us the best tool for this in Disk Utility. Using the Erase function, we can select 'Security Options' and hit the radio button for 'Zero Out Data'. Hit 'OK' and then Erase and the process will start. This can take over an hour with large drives and you will want to monitor how long it actually takes via the progress bar.
Zero Multiple Drives Simultaneously
A great little trick to know: you can run multiple copies of Disk Utility and do more than one drive at a time. This will save you considerable time if you are zeroing out a monster 8 or 10 drive RAID array. If you hold down the Option key you can drag copy Disk Utility to a second location. 'Option' makes it a copy process, without the Option key you are only moving the application. As long as you choose a different location or folder to copy to you can run 3 or 4 copies all at once.
On Port Multiplier Systems we would recommend you only zero a maximum of three drives simultaneously per port multiplier, two is best. More than that you will effect the time each drive takes because of too many accesses over a single data channel. Because we want to monitor each drive, and its performance in relation to all other drives (hopefully identical), we want to limit the variables as much as possible.
With Firewire you can only zero a single drive at a time because of bus constraints. Two drives simultaneously zeroed will take twice as long as one drive on a Firewire bus. Keep it simple on your Firewire drives and only zero one at a time.
Keep an eye on how long the drives each take to Zero. At the bottom of the Disk Utility window is an estimated time to completion. Each drive should both estimate, and in actuality take, the same amount of time within a minute or two unless other processes are hogging resources or bus access. Here's what you will see at the bottom portion of a Disk Utility window during a zero all erase:
You will find the effort and time to be well spent. Ensuring, to the best of our abilities, that our data is as safe as we can make it is of first priority. We have found this procedure to be the best way to accomplish that. Beating back the data loss gremlins is righteous duty.
The Gurus Certify This Guide Rules!