RAID 1, also known as disk mirroring, is a redundancy technology that allows you to store duplicate copies of your data on two or more hard drives. This protects your data in case one of the drives fails. With RAID 1 using two 500GB drives, the total usable space would be 500GB.
What is RAID 1?
RAID stands for “Redundant Array of Independent Disks”. It is a data storage technology that combines multiple physical drives into a single logical unit. The drives work together to increase performance, capacity, and reliability beyond what a single drive can provide.
There are several levels of RAID, with different configurations and use cases. RAID 1 is one of the most basic and popular RAID levels.
With RAID 1, data is written identically to two or more drives in the array, a process known as “mirroring”. If one drive fails, the other has an exact copy of the data to keep the system running with no downtime or data loss. RAID 1 provides fault tolerance and increases read performance since data can be read simultaneously from both drives.
RAID 1 Configuration
A basic RAID 1 setup requires at least two physical drives of equal capacity. When data is written to the RAID 1 array, it is written to both drives at the same time, creating a mirrored set.
For example, with two 500GB drives in a RAID 1 configuration, data is written to both drives simultaneously. If one drive fails, the other contains an exact copy of the data to keep the system operational.
RAID 1 Usable Space
One key disadvantage of RAID 1 is that usable space is reduced, because the data is duplicated on both drives. With two 500GB drives, the total capacity is 1000GB but the usable space is only 500GB since each drive contains the same data.
In general, with RAID 1 using N drives of equal capacity, the total usable space will be the capacity of a single drive. For example:
- 2 x 500GB drives = 500GB usable space
- 2 x 1TB drives = 1TB usable space
- 4 x 2TB drives = 2TB usable space
The usable space does not increase, it remains equal to the capacity of one of the mirrored drives. The additional drives provide fault tolerance through duplication, but do not expand the usable space beyond a single drive’s worth of storage.
Advantages of RAID 1
Although usable space is reduced, RAID 1 offers several key advantages:
- Fault tolerance – Data remains accessible even if one drive fails. The failed drive can be replaced and rebuilt without downtime.
- Increased read performance – Data can be read simultaneously from both disks for faster reads.
- Simple configuration – RAID 1 is easy to setup and manage compared to other RAID levels.
Disadvantages of RAID 1
The tradeoffs to consider with RAID 1 include:
- Reduced capacity – Usable space is limited to the capacity of one drive.
- Write performance – Write speeds are slower compared to a single drive since data has to be written twice.
- Higher cost – Requires at least two drives, increasing overall storage costs.
When to Use RAID 1
Here are some examples of use cases where RAID 1 can be beneficial:
- Storing critical data that cannot have any downtime or data loss.
- Database servers that need enhanced read performance.
- Small business servers that require fault tolerance with minimal complexity.
- Workstations that need to maximize uptime by reducing risk of drive failure.
Alternatives to RAID 1
If the capacity and cost limitations of RAID 1 are too restrictive, alternatives such as RAID 5, RAID 6, or RAID 10 provide more usable space for the same number of drives. However, they have higher complexity, lower read performance, and potential for longer rebuild times when recovering from a failed drive.
Another option is to use a cloud backup service or backup software to make copies of your data to external drives. This doesn’t provide the same real-time duplication and fault tolerance as RAID 1, but can be part of an overall backup strategy.
RAID 1 Use Cases and Examples
Here are some examples of how 500GB RAID 1 arrays could be used:
| Environment | Use Case |
|---|---|
| Small office | Using two 500GB drives in RAID 1 to store critical office documents, databases, and shared files accessed by employees. 500GB provides adequate capacity with room for growth. |
| Graphics office | Storing active graphic design files and assets on a 500GB RAID 1 array for enhanced read speeds. Project archives are stored on a separate non-RAID drive. |
| POS system | A point-of-sale server with a 500GB RAID 1 array to store transaction and inventory databases. Duplication ensures uptime if a drive fails. |
These examples maximize fault tolerance and uptime for critical data, while 500GB remains adequate for their capacity needs.
Expanding RAID 1 Arrays
If you outgrow a 500GB RAID 1 array, the space can be expanded by:
- Replacing both existing drives with larger drives.
- Keeping one existing drive and adding a larger second drive (drives will use the capacity of the smaller drive).
- Converting to a nested RAID 1 setup, with two arrays using 500GB each for 1TB total space (with some additional complexity).
A direct replacement with larger matched drives is recommended for simpler expansion. For example, you could upgrade to two 2TB drives to substantially increase the usable RAID 1 space to 2TB.
RAID 1 Performance
RAID 1 provides excellent read performance, as data can be read simultaneously from both mirrored drives. However, write performance suffers due to the dual-write operation.
Here are sample sequential read and write speeds for 500GB HDD RAID 1 array versus a single 500GB HDD:
| Operation | RAID 1 with 2 x 500GB HDD | Single 500GB HDD |
|---|---|---|
| Sequential Read | 160 MB/s | 80 MB/s |
| Sequential Write | 80 MB/s | 160 MB/s |
As you can see, RAID 1 read speed is double that of a single drive, while write speed is reduced. Performance can be further enhanced by using high-RPM drives or SSDs instead of HDDs.
RAID 1 Reliability
One of the main benefits of RAID 1 is excellent reliability due to the mirrored drives. Statistical models estimate an annual failure rate for a single 500GB HDD around 2-4%.
With RAID 1, a failure only occurs if both drives fail simultaneously. The probability of this on a 2-drive array is the product of the individual failure rates:
- If each drive has 4% annual failure rate, the array failure rate is 4% x 4% = 0.16%
- At 2% individual failure rate, the array failure rate is 2% x 2% = 0.04%
Therefore, RAID 1 dramatically improves the reliability and uptime of your storage system. Rebuilding a failed drive quickly restores redundancy.
RAID 1 Rebuild Time
When a drive does eventually fail in a RAID 1 array, a rebuild will be required to restore full redundancy. The time for this is proportional to the size of the drives.
For two 500GB HDDs, rebuilding a failed drive would take 2-5 hours typically. Larger drives or slower interfaces would increase this time. During a rebuild, failure of the second drive would result in data loss.
To minimize downtime, replacing failed drives quickly is recommended. Some RAID controllers also support hot-swapping drives without interruption.
Software vs Hardware RAID 1
RAID 1 can be implemented through either hardware or software solutions:
- Hardware RAID – Uses a dedicated RAID controller card and firmware managed RAID configuration. Offloads processing overhead from the CPU.
- Software RAID – Managed directly by the operating system and drives appear as a logical volume. No special hardware required.
Hardware RAID provides some performance advantages, as well as the ability to still boot if the operating system fails. But software RAID is cheaper and easier to manage. Both options work effectively for RAID 1 arrays.
RAID 1 Implementation
To implement RAID 1, you need:
- 2 or more drives of the same capacity.
- RAID controller (hardware RAID) or operating system support like Windows Disk Management (software RAID).
- Cables and enclosure to connect the drives if installing internally.
Then you can select the drives, specify RAID 1 as the desired configuration, and initialize the array. The operating system will see it as a single logical drive.
Managing and Monitoring RAID 1 Arrays
Best practices for managing RAID 1 arrays include:
- Monitoring drive health to detect failures early.
- Replacing failed drives as quickly as possible.
- Running periodic surface scans to identify pending drive issues.
- Having spare drives ready for rapid rebuilding if a failure occurs.
- Scrubbing arrays periodically to correct data inconsistencies.
This helps maximize the fault tolerance benefits and minimize the risk of data loss.
Conclusion
In summary, a two drive 500GB RAID 1 array provides 500GB of usable storage by mirroring data between drives. The advantages of RAID 1 include fault tolerance, improved read speed, and simple configuration. The tradeoffs are reduced capacity, slower writes, and higher cost than a single drive.
RAID 1 is ideal for storing critical data that requires high availability and uptime. With proper drive replacements and array management, it provides excellent reliability compared to a single drive. While you halve your total capacity, the duplication of data ensures continuous operations if a drive fails.