What is RAID?
RAID stands for “Redundant Array of Independent Disks.” It is a data storage technology that combines multiple physical disk drive components into one or more logical units for the purposes of data redundancy, performance improvement, or both [1]. RAID takes advantage of the parallelism of multiple disks to enhance data transfer rates and provide fault tolerance.
The most common RAID levels include:
- RAID 0 – Also known as disk striping. Data is distributed across multiple disks with no redundancy. Offers fast performance but no fault tolerance.
- RAID 1 – Also known as disk mirroring. Identical copies of data are stored on two separate disks. Provides redundancy but reduced storage capacity.
- RAID 5 – Data is striped across multiple disks with parity information distributed across all disks. Can withstand the failure of one disk.
Other RAID levels (RAID 2, 3, 4, 6, etc) provide different combinations of performance, capacity, and fault tolerance depending on the implementation.
[1] https://www.techtarget.com/searchstorage/definition/RAID
Why use RAID?
RAID offers several key benefits that make it an attractive storage solution for many users:
Increased redundancy
One of the main reasons to use RAID is to protect against data loss due to drive failures. By spreading data across multiple disks, RAID provides redundancy so that if one drive fails, the data can still be reconstructed from the remaining drives (DiskInternals, 2023).
Better performance
Many RAID configurations can increase read and write speeds by distributing the workload across multiple disks. This is especially beneficial for high-demand server environments (Xinnor, 2023).
Ability to recover data if a drive fails
Thanks to redundancy, a failed drive in a RAID array can be replaced and the data rebuilt without significant downtime. This protects against potential data loss in the event of a disk failure.
Checking for RAID in Windows
You can check for RAID arrays in Windows by using the Disk Management utility. This allows you to view the disks installed on your system and identify any that are configured as RAID volumes. Here are the steps to check for RAID in Windows:
1. Open the Disk Management utility by right-clicking the Start menu and selecting “Disk Management”. You can also search for it in the Start menu.
2. In the Disk Management window, look at the various disks listed on the lower half. Check their “Type” column.
3. Any disk marked as “Dynamic” is part of a RAID array. The status will specifically indicate “RAID-0 Volume” or other RAID levels.
4. You can also look for multiple disks with a healthy status but without any drive letters assigned. This indicates the disks are part of a RAID array.
5. Hover over each Dynamic disk to verify the RAID status in the details at the bottom of the Disk Management window.
This allows you to easily check for and identify RAID arrays present in Windows. Using Disk Management, you can view RAID information like the RAID level, stripe size, operational status, and the physical disks included in the array. If you don’t see any Dynamic disks, then RAID is likely not configured on your Windows system.
Checking for RAID in Mac OS X
Mac OS X provides some simple ways to check for RAID configuration using the built-in Disk Utility application. Here are a couple things to look for in Disk Utility to identify RAID:
Using Disk Utility to check for RAID sets – Open Disk Utility and look in the sidebar for any groupings of disks labeled with “RAID” and a number, like “RAID 0” or “RAID 1.” These groupings indicate the disks are configured as a RAID set. [1]
Checking for volumes with RAID icons – Click on any volumes in Disk Utility and look for the RAID icon in the top right corner. The icon will be multiple interlocked rings labeled “RAID” if the volume is part of a RAID set. [2]
Checking for RAID in Linux
There are a couple ways to check for RAID setup in Linux operating systems.
Using mdadm
The mdadm tool can be used to scan for and display information about RAID arrays. For example, running sudo mdadm --detail --scan will show details on any RAID arrays detected such as array status, RAID level, and component disks 1.
Checking /proc/mdstat
The file /proc/mdstat contains status information on RAID arrays. Viewing this file with cat /proc/mdstat will show any active arrays, their RAID levels, and component disks. This provides a quick overview of the RAID setup on a Linux system 2.
Additional RAID configuration details and tools are also available on Linux, but mdadm and /proc/mdstat provide a simple starting point for detecting and confirming RAID status.
Identifying RAID controller
The first step in identifying your RAID controller is to check Device Manager in Windows. Open Device Manager and expand the “Storage controllers” section. Any RAID controller cards will be listed here, along with details on the model and chipset.
For example, you may see an entry for “RAID Controller XYZ” with a model number and other specifics. This will tell you the brand and exact hardware model of the RAID card.
Onboard RAID controllers integrated into the motherboard can also be viewed in Device Manager. These will often have chipset names like “Intel SATA RAID Controller.”
In Linux, you can use the lspci command to list PCI devices, which will include any RAID controller cards. The brand and chipset details will be shown.
If you know the model of your motherboard, you can check the manufacturer’s documentation to determine if onboard RAID is enabled and which chipset it uses.
Overall, Device Manager in Windows or the lspci output in Linux will provide the quickest and most definitive way to identify the current RAID controller. Checking the chipset and model details will give you specifics on the hardware brand and capabilities.
Viewing RAID configuration
There are a couple ways to view your RAID configuration depending on your operating system.
On Windows, you can view your RAID configuration by entering the RAID BIOS/firmware upon boot. To do this, restart your computer and press the hotkey to enter the BIOS/firmware settings, often Delete or F2 during boot. Then navigate to the section related to RAID configuration. Here you will see details on your RAID arrays. You can also use Windows built-in Disk Management utility. Right click the Start menu and select Disk Management. This will show disks and volumes including RAID arrays.
On Mac OS X, you can use the Disk Utility application to inspect RAID configurations. Launch Disk Utility, select the RAID volume and click Info. This will show the RAID type and status.
On Linux, install the mdadm utility if not already present. Run sudo mdadm –detail /dev/md0 to see details on RAID arrays. The /proc/mdstat file also contains RAID info.
Third party RAID management software like those from storage vendors may also be used to view and manage RAID across operating systems.
You can also enter the RAID BIOS/firmware settings directly during boot, before the OS loads, to view the raw RAID configuration. The hotkey varies but is commonly Delete, F2, Ctrl+I, Ctrl+R, or Alt+R. This allows viewing and configuring RAID settings at the controller level.
Verifying RAID status
Verifying the status of your RAID configuration is important to check for any errors or failed drives. There are a couple ways to verify RAID status:
Check for any failed or inconsistent drives using RAID management software or disk utility tools. Most will indicate drive errors clearly. On Windows, you can use Disk Management. On Linux, mdadm is a common RAID tool with status commands like mdadm --detail /dev/md0. Mac OS has Disk Utility.
Review the sync status, which indicates if the RAID data and parity is fully updated across the array. Out of sync usually means a rebuild is in progress after replacing a failed drive. You want to see the RAID as fully synchronized/rebuilt for full redundancy. On Windows, check the status in Disk Management. Linux mdadm will show sync status. On Mac OS, verify in Disk Utility.
Running data scrub or verify operations on the RAID is also recommended periodically to proactively catch any inconsistencies. This can be done through OS tools like chkdsk on Windows or third-party RAID software utilities.
If you do see errors, you will likely need to troubleshoot further or contact the RAID controller or disk vendor for next steps, which may involve replacing failed drives and rebuilding the RAID.
Troubleshooting RAID Issues
RAID arrays can experience issues like degraded performance, failed drives, or complete failure. Here are some tips for troubleshooting common RAID problems:
Fixing Degraded Arrays
A degraded array has experienced a disk failure but is still partially operational using the remaining disks. To fix a degraded array:
- Identify and replace any failed hard drives. Use RAID monitoring software or your RAID controller to locate the failed drive.
- Once the new drive is installed, the array will rebuild itself. This can take several hours depending on the RAID level and drive sizes.
- Monitor the rebuild process in your RAID software. Do not interrupt the rebuild as this can cause data loss.
Rebuilding Failed Drives
If a drive in the array completely fails, rebuild it by:
- Replacing the failed drive with a new, identical drive.
- Allowing the RAID controller to rebuild the drive automatically.
- Monitoring the rebuild process until completion.
The required steps vary by RAID level:
- RAID 0 has no redundancy, so a failed drive causes complete data loss.
- RAID 1 can continue operating in a degraded state on one drive until the failed drive is rebuilt.
- RAID 5 and 6 use parity data on the remaining drives to rebuild a failed drive’s data.
Restoring from Parity in Case of Failure
If multiple drives fail in RAID 5, 6, or 10 arrays, parity data on the remaining drives can recreate the missing data. To restore parity:
- Replace all failed drives to return the array to a redundant state.
- Allow the rebuild process using parity data to complete.
- If too many drives fail, resulting in complete data loss, restore from backups.
Consult your RAID controller’s documentation for the detailed steps to recover from multiple drive failures.
Alternatives to hardware RAID
There are several alternatives to traditional hardware RAID that provide data redundancy without requiring a specialized RAID controller.
One option is software RAID. This uses the operating system and software to handle the RAID tasks like striping and mirroring data across drives. Software RAID doesn’t require special hardware and can work with inexpensive commodity drives. Most operating systems like Windows, Linux, and MacOS have built-in software RAID capabilities. While flexible and cost-effective, software RAID may impact performance more than hardware RAID since the CPU has to handle the RAID overhead.
Cloud storage services can also provide redundancy for important data. By replicating files to cloud storage like Dropbox, Google Drive, or Backblaze, you can protect against failures of local drives. The cloud services transparently handle making redundant copies of your data across their servers. The downside is you must have internet connectivity to access cloud data. There are also ongoing costs for paying for the storage space used.
Finally, a basic but essential redundancy technique is regular backups. Services like Apple Time Machine, Windows Backup, or third-party backup software create copies of your important files on external drives. While backups require more manual intervention to restore compared to RAID, they protect against catastrophic failures like accidental deletion. Backups also provide an “offsite” copy if the primary storage is damaged or stolen. Some recommend combining automated backups with drive pooling solutions like DrivePool for flexible redundancy without RAID.