You should NOT run the CHKDSK command on a degraded RAID array (one or two disk failure), as it can mark healthy sectors as “bad”, thus causing irreversible data loss. In case the drive failure/s have happened due to bad sectors on the drive or for any other reason (discussed below), use a professional RAID data recovery instead. CHKDSK at this stage will not help you recover data anyhow, as it doesn’t read RAID parity, stripes, or the logical arrangement of the member drives. It works on individual drives/volumes. Hence, running it would be fatal for the entire data if it encounters even a bit of corruption or inconsistency.
Understanding the Basics — CHKDSK and Degraded RAID Array
Before we understand why running a CHKDSK is bad for a degraded RAID, let’s first clear our basics – what exactly is a degraded RAID array, and what is CHKDSK?
What does “RAID Array Degraded” State Actually Mean?
A RAID array consists of multiple physical drives working together as a single logical volume. In configurations like RAID 5 or RAID 6, where data parity – a piece of binary data calculated and stored as ‘blocks’ for disk redundancy – is involved, a RAID array with failed member drives (within the set limits) goes into the “degraded” state. The array doesn’t immediately fail, but it becomes quite risky to keep it running. This is because a subsequent RAID disk failure may happen, resulting in complete RAID array failure.
Tabulated below are “Degraded” states across some popular RAID Levels:
| RAID Array | Type of Storage Technique | Disk Failure Limit for Degraded State | What it Means |
| RAID-1 | Mirroring | 1 | Can run on the remaining disk drive |
| RAID-5 | Striping + parity | 1 | Can sustain a single-disk failure; second drive failure will result in complete data loss |
| RAID-6 | Striping + double parity | 2 | Can sustain two disk failure; third drive failure will result in complete data loss |
| RAID-10 | Striping in each mirrored set | 1 in each mirrored set | Can run with 1 disk failure in each mirrored pair, a second drive failure in the same mirrored will result in complete data loss |
What is CHKDSK Utility?
Check Disk or CHKDSK is a disk monitoring utility that comes in-built with Windows OS. It is a vital tool that is used to scan and fix numerous storage drive-related issues, such as –
- Corrupted file system or metadata
- Corrupted MFT or Master File Table
- Bad/damaged sectors
- Misaligned time stamps
- Incorrect file size data and security flags
CHKDSK is a simple command that starts by scanning & checking the file system of a drive, followed by data integrity and file metadata. Alongside these checks, it also looks for logical errors, corrupted entries in MFT, misaligned time stamps, etc., and repairs them right away, without affecting the drive’s data.
CHKDSK can be used to fix the underlying causes behind a malfunctioning HDD. CHKDSK repairs soft errors by rewriting incorrect data and hard errors by marking a section of the disk that is damaged ‘bad.’
What Actually Happens when you Run CHKDSK on RAID Array that is Degraded?
When you run CHKDSK on a degraded RAID array via CMD, the command sees the member drives as a single logical storage volume. It doesn’t understand that the drives are logically connected. Depending upon the parameters used alongside, the utility scans each of the member drives separately for corruption in the file system structure, MFT, etc. When it encounters the file system or file-level corruption. It marks all the problematic bits on the drive containing that data as unreadable.
In case of a degraded RAID array, incorrect use of the CHKDSK command can do more harm than good. It looks for consistency, which might be missing due to data striping/parity or a failed member drive. Because of this, it flags those bits for corruption and updates their status in MFT. This renders the data (or a part of the data) inaccessible, thus permanently destroying the data that could have been recovered.
How CHKDSK Works? (The Breakdown of the Failure Chain)
- CHKDSK runs and looks for any inconsistencies in the files/file system
- Reads the data from the degraded RAID disk and flags it for inconsistencies
- Based on the parameters entered by the user, mark the bits as “corrupted” and inaccessible
- Data in those bits gets lost
Why this Damage is Often Irreversible?
Below, we have listed some reasons why running CHKDSK on RAID that is in a degraded state is not a good strategy.
1. CHKDSK Overwrites the Exact Metadata that Recovery Tools Need
RAID reconstruction software depends on superblocks, stripe headers, and partition metadata to identify member order, stripe size, and parity rotation. CHKDSK finds this information inconsistent and overwrites it with zeros.
2. It Compounds the I/O Stress on the Remaining Member Drives
Every time the controller reads from a stripe that includes a failed member disk, the controller runs the XOR operation on the remaining drives to compute the missing data. On top of this, running CHKDSK adds an additional load of a full-volume read-and-write pass on the degraded RAID array — dramatically increasing the chance of another drive failing mid-scan.
3. It May Mark Healthy Drives as Unreadable
CHKDSK can flag healthy sectors on member drives as having errors because of striped data or distributed parity. Its sector-level repair attempt can mark these sectors as “bad.” A drive with a significant number of bad sectors should not be used.
Safe Action Plan for a Degraded RAID Array
As the RAID management system (for hardware RAID) or the system (for software RAID) marks a RAID disk “degraded”, do not run CHKDSK or any third-party disk repair software. Instead, follow the steps in the given order:
- Cease All Write Operations: Do not use the degraded RAID array to save or retrieve any files. Every write operation narrows the chances of successful data recovery.
- Identify the Failed Drive/s: Use the RAID controller’s dedicated management software (eg. Intel RST, Broadcom WebBIOS, and more) or the BIOS to verify which member disk has caused the array to go in the “degraded” state.
- Check S.M.A.R.T. Status of Remaining Drives: While in the RAID controller’s management software, verify the health of other member disks. Look for the following – high reallocated sectors, pending sectors, or CRC errors. If any drive shows signs of failure, clone or replace it first to avoid a second failure during recovery or rebuild.
- Use a Professional RAID Data Recovery Software to Recover Important Data: If you can still access data on the RAID array, prioritize retrieving important files – invaluable business/work files, financial documents, IDs, etc. To do this, use a professional RAID data recovery software like Stellar Data Recovery Technician. It is a powerful DIY application that provides a safe environment to recover data from degraded or crashed RAID setups. With this tool, you can retrieve all kinds of files from RAID-0, RAID-5, and RAID-6 arrays. After the recovery, back up the retrieved data immediately to an external storage device or cloud.
- Hot-swap or rebuild the degraded RAID Array: The final step – try to rebuild the degraded RAID array. Try to hot-swap the failed disk/s (if supported) or rebuild the array using new disk drives from scratch.
Here are some highlights of this software:
- Restores data from HDDs, SSDs, Flash drives, Optical media, 4K drives, RAID arrays, and RAW volumes
- Facilitates recovery from a crashed or unbootable Windows PC using a bootable media drive
- Recovers files from BitLocker-encrypted drives
- Helps track various S.M.A.R.T. attributes of drives: including health, performance, and temperature
- Retrieves all types of data including documents, images, videos, audio files, mailbox files (PST, MBOX, OLM, etc.)
- Helps create disk images or clones of drives with bad sectors or corrupted file system
- Lets users verify recovered files before restoring them
- Works on Windows 11, 10, 8.1, and 8 systems
- Supports NTFS and EXT-2/3/4 formatted drives
Note: If you encounter any physical or logical signs of failure – clicking or grinding noises, slow response time, S.M.A.R.T. errors – stop using it right away and contact a professional data recovery lab.
Real-World Scenario: How Running CHKDSK Almost Endangered the Whole RAID Server
Let’s have a look at an instance of running CHKDSK on a problematic RAID array.
Situation
A Reddit user – u/Carburetors_are_evil, posted about a RAID 5 array configured using 4x 7200rpm 1TB drives, in a Dell Poweredge tower server. There was a sudden power outage, due to which it was running very slow after. The OP (user) ran a CHKDSK command with the /r parameter, which got to 10% and then was stuck there for almost 16 hours. Though, after a long wait, the scan finished in just 10 minutes.
What could have gone wrong?
Had there been any bad sectors on the drive, the CHKDSK would have marked them as inaccessible, thus rendering the data as permanently lost. Moreover, the amount of stress put on the member drives while scanning could have introduced more bad sectors – making the situation a lot worse.
What should have been done?
Instead of running the CHKDSK command, user should have check the RAID array management software for any issues. Then, used a professional recovery software to retrieve important files, if any error is found. And then attempt to fix the issue.
Observation
User didn’t have a backup of the files on the RAID. The situation could have gone south in no time, resulting in data loss. Hence, it is always recommended to have a backup of important files on other storage media or cloud. If possible, follow the 3-2-1 backup strategy.
EndNote
CHKDSK is a useful command-line utility for scanning individual disks for any file system inconsistencies. So, it cannot work on RAID arrays. When a RAID disk is degraded — be it RAID-1 or RAID-5/6 — the approach is simple: stop writing data on it, identify the failed member disks, check for S.M.A.R.T. status, and use a professional RAID recovery software such as Stellar Data Recovery Technician – to recover vital data before you rebuild/hot swap the disk(s).
It is quite understandable to fix things quickly. But running a file system repair tool on a volume whose underlying architecture is not supported, is a risky step. If you’re unsure of what to do next after getting the “degraded RAID array” status on your screen, contact a professional.
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