Why should I certify a new disk—don’t they get tested at the factory?

Most modern disks only receive limited testing during the manufacturing process. They are tested to confirm they can start and stop reliably and read and write data correctly — but this testing only covers a small sample of sectors, not the entire disk surface. Manufacturers expect that users will discover faulty sectors as they use their drives. On a large drive, it may take a year or more of normal use before you ever reach a defective area — by which time you may have already stored important files there.

SoftRAID’s disk certification tests every single sector on the drive. The certify process writes random data to every sector and reads it back to verify the data is identical — ensuring the drive can reliably store and retrieve data across its entire surface. The final pass writes zeros, returning the drive to “as new” condition.

We recommend a 3-pass certify for all new drives. This gives you the highest confidence that your drive is fully reliable before you trust it with your data.

Important: Certifying a disk will permanently erase all data on it.

How long does certification take?

Certification is thorough but time-consuming. As a general rule:

• HDDs: approximately 1 day per 2TB of capacity (a 4TB drive can take ~48 hours)
• SSDs: a 2TB SSD typically takes 4–8 hours for a 3-pass certify

For detailed estimates by drive type and enclosure, see our FAQ: How long does it take to certify a disk?

What about certifying used or reused disks?

You can — and should — certify a used disk before reusing it in a different Mac or for a different volume. Certifying a used disk confirms it is still fully reliable and has not developed any bad sectors since it was last tested. The same rules apply: certification will erase all data on the disk, so back up anything you need first.

If you keep a spare drive on hand for emergencies, it should be re-certified periodically to ensure it is ready for immediate deployment when needed. See our FAQ: I have a spare drive for my RAID — “I have a spare drive for my RAID — how often should I re-certify it?”.

What about SSDs and NVMe drives?

Yes — we strongly recommend certifying all flash media as well. SSDs can have unreliable regions just like HDDs, and certification also “refreshes” the drive, restoring write performance to optimal condition. See our FAQ: “Always certify a disk before using it” for full details on certifying flash media.