RAID 0 is popular with Mac users who work with video, photography and audio, because it is fast. Two or more drives are combined into one large volume, and every file is split across all of them. The catch is that RAID 0 has no redundancy at all: if any one drive in the set fails, the whole volume stops mounting. When that happens, the first few things you do decide whether the files come back easily, with difficulty, or not at all.
Where Mac RAID 0 sets come from
Mac users usually end up with a striped set in one of three ways:
- Disk Utility. macOS can create a RAID set (“striped” is RAID 0) from two or more drives, often in a multi-bay USB or Thunderbolt enclosure.
- SoftRAID. OWC’s SoftRAID software creates RAID 0 volumes, and is common on OWC ThunderBay and similar enclosures.
- Hardware RAID enclosures. Many Thunderbolt and USB-C desktop RAIDs, including G-RAID, LaCie and Promise Pegasus units, are often set up as RAID 0 for speed. Here the striping is done by a controller inside the box, not by macOS.
Knowing which one you have matters, because it changes what “failed” means and what a recovery has to rebuild.
Common reasons a striped volume disappears
- One drive fails. The most common cause. A single drive develops bad sectors, a mechanical fault or an electronic failure, and the set can no longer be read.
- The enclosure fails, not the drives. A dead power supply, a failed Thunderbolt or USB bridge board, or a faulty RAID controller makes the volume vanish, even though all the drives are healthy.
- Software or a macOS update. After an upgrade, a software RAID driver may need to be updated or re-approved before the volume will mount.
- Human error. The set was deleted, recreated or initialized by mistake, or drives were moved to different bays.
Safe checks you can do
These don’t write anything to the drives:
- Check the power supply, cable and port. Try a different Thunderbolt or USB cable and port.
- If you use SoftRAID, check that it is up to date for your version of macOS, and look in System Settings, Privacy & Security, for any blocked software that needs approving. A volume that disappeared straight after a macOS update often comes back this way.
- Open Disk Utility and choose View, Show All Devices. Note which drives appear and whether any is missing or shows the wrong size. Don’t click anything else.
If those checks don’t bring the volume back, stop there.
What not to do
- Don’t recreate the RAID set. Creating a “new” striped set over the same drives, in Disk Utility, SoftRAID or an enclosure’s utility, writes new RAID information and often erases the volume. It is the most common way a recoverable RAID 0 becomes much harder to recover.
- Don’t initialize or erase any member drive, even if macOS says it “isn’t readable” and offers to.
- Don’t run First Aid again and again. On a set with a failing drive it can’t fix the underlying fault, and the repeated reading stresses the weak drive.
- Don’t swap drives between bays or enclosures to “see if it works”. Label each drive with its bay position before removing it, so the original order is known.
- Don’t keep a clicking or slow drive powered while you search forums. Every hour of use can make the failing drive worse.
How a RAID 0 recovery works
Because every file is spread across all the drives, a recovery needs every member of the set, including the healthy ones. Each drive is first copied sector by sector, with any failing drive repaired or imaged using specialist hardware so it isn’t stressed further. The striped volume is then rebuilt from those copies, not from the original drives. That means working out the drive order and the stripe size, then reading the file system (usually APFS or HFS+ on a Mac) from the rebuilt image. If the enclosure failed but the drives are fine, the rebuild can often be done without repairing anything. The more of the original striping information that is still intact, the quicker and more complete the recovery.
Our NAS and RAID recovery page covers the enclosures and RAID types we work with, including SoftRAID and Disk Utility sets.
Next time: RAID 0 is not a backup
RAID 0 doubles the speed and also roughly doubles the risk, because it fails if any drive fails. If you rely on a striped volume for working files, keep a separate backup on another drive. That can be Time Machine, a cloned copy, or a backup NAS, and you should check that it actually restores. If an external backup drive is the thing that has failed, see external and Time Machine drive recovery.
Talk to us before you try anything else
If your striped volume has disappeared, power it down, label the drives and call us on 020 7394 2525. Inspection is free, and you get a fixed quote before any work starts. Our prices page shows the standard ranges, or you can send us the details. You are welcome to drop off at our lab at 80 Willow Walk, London SE1, Monday to Saturday, 9am to 6pm.