What is RAID 1?
RAID 1 is a standard RAID (Redundant Array of Independent Disks) configuration that uses disk mirroring to create an exact copy of data on two or more disks (Computerworld). Disk mirroring means writing identical data across multiple disks, so if one disk fails, the data is preserved on the other mirrored disks. RAID 1 provides redundancy and fault tolerance by protecting against disk failures, but it does not provide increased storage capacity since the same data is duplicated on all the disks.
With RAID 1, any write operations will be carried out on all mirrored disks simultaneously. For read operations, the workload can be distributed across the disks which can improve read performance. However, write performance does not improve as every write must be completed on all disks (PCMag). The key benefit of RAID 1 is high availability and redundancy. If one disk fails, the system can instantly failover and continue operating using the remaining mirrored disk(s). This makes RAID 1 well suited for mission critical systems that require constant uptime.
Pros of RAID 1
RAID 1 offers several key advantages that make it a popular RAID configuration:
Data redundancy and protection against drive failure – With RAID 1, data is written identically to two or more drives simultaneously. If one drive fails, the data remains intact and accessible on the other mirrored drive(s). This provides high fault tolerance and protection against data loss from a single drive failure (Liquid Web, IONOS).
Improved read performance – Since the same data is stored on multiple mirrored drives, read requests can be distributed across drives for better performance. RAID 1 provides faster reads compared to a single drive (Stellar Info).
Simple to understand and implement – The mirroring concept in RAID 1 is straightforward to comprehend. It’s also relatively easy to setup and configure vs. more complex RAID levels (Liquid Web).
Cons of RAID 1
One of the main drawbacks of RAID 1 is that it offers no fault tolerance if the configuration only uses two disks. If one of the disks fails, there is no redundancy and the system will go down. This lack of fault tolerance with just two disks increases the risk of downtime.
RAID 1 is also more expensive compared to RAID 0 or a single disk setup, since RAID 1 requires at least two disks for the same usable capacity. With each additional mirror added, the cost goes up proportionally. The tradeoff for better redundancy is higher hardware costs.
Performance, specifically write performance, may suffer with RAID 1 versus a single disk. Writes have to go to multiple disks simultaneously, which can create a bottleneck. The controller has to write the data across all disks in the array, reducing overall write throughput compared to a single disk.
According to one analysis, “RAID 1 configurations provide excellent read performance but poor write performance.”1 The multiple write penalty of mirroring data can noticeably reduce throughput for write-heavy workloads.
Ideal Uses for RAID 1
RAID 1 can be an ideal RAID level for certain use cases that require redundancy for critical data or high uptime for server applications. According to Petri.com, “For any use case where you need data to be ultra-reliable, you’ll want to use RAID 1.”
Some of the most common ideal uses of RAID 1 include:
- Database servers – Since most database servers require high uptime and redundancy, RAID 1 is frequently used. The mirrored drives provide fault tolerance if one drive fails.
- Business critical systems – For networks and servers that need to ensure continuous uptime, RAID 1 provides the redundancy to minimize downtime.
- Small servers – For a server with only space for two drives, RAID 1 allows you to mirror them for redundancy.
In summary, any application where downtime is unacceptable and redundancy is critical should consider using RAID 1. The dual mirrored drives tolerate a single drive failure while providing continuous availability.
Alternatives to RAID 1
While RAID 1 offers redundancy through mirroring, there are other RAID configurations that provide different tradeoffs between capacity, performance, and fault tolerance. Two popular alternatives are RAID 5 and RAID 10.
RAID 5 stripes data across multiple drives and uses distributed parity to provide redundancy. Compared to RAID 1 which cuts storage capacity in half, RAID 5 only sacrifices 1 drive’s worth of capacity for parity. This allows you to get better overall capacity while still protecting against a single drive failure. RAID 5 can also provide better write performance than RAID 1 since writes are striped across multiple drives.[1]
RAID 10 combines mirroring and striping for both redundancy and increased performance. By striping across mirrored drive pairs, RAID 10 can deliver faster reads and writes compared to RAID 1. However, it also requires at least 4 drives to implement, so it is more costly than RAID 1. Still, for use cases that demand both speed and redundancy, RAID 10 is a popular alternative.[2]
Backups and snapshots also provide redundancy without needing full RAID configurations. Solutions like file-based backup or cloud backups can efficiently protect important data in case of disk failures. Snapshots capture the state of a storage volume at a point in time, allowing you to roll back in case of corruption or errors. For some use cases, these options may provide sufficient protection without needing to sacrifice capacity to redundancy. [3]
Implementation Tips
When setting up RAID 1, there are some best practices to follow for optimal performance and protection:
Use identical drives from the same manufacturer – RAID 1 works best when the mirrored drives are the same make and model. This helps ensure consistency in performance and lifespan across the array.
Consider hot spares to automatically rebuild if a disk fails – Adding hot spare drives that are not part of the RAID 1 array can allow the system to automatically rebuild the mirror if one of the main drives fails. This reduces downtime.
Monitor disk health – Keep an eye on S.M.A.R.T. data and other disk health metrics to watch for signs of impending failure. Replacing disks proactively can prevent array degradation.
For more tips, see this in-depth guide on best practices for setting up RAID 1.
Sample RAID 1 Configurations
Here are some common RAID 1 configurations to illustrate how disk mirroring can be implemented with different drive setups:
2 x 2TB Disks for 2TB Redundant Storage
A basic RAID 1 can be created with just two identical disks, like two 2TB hard drives. The total storage capacity would be 2TB, since each drive fully mirrors the other. This provides full redundancy, so if one drive fails, the data is still intact on the other drive. The downside is no additional capacity is gained.
4 x 120GB SSDs for 480GB Fast Redundant Storage
For applications requiring high speed, like a database server, RAID 1 can be implemented using SSDs. With four 120GB SSDs, two mirrored pairs can be created for a total of 240GB mirrored capacity. This would provide the redundancy of RAID 1 along with the speed boost of SSDs. The total usable space would be 480GB across the four drives.
Benchmarks of RAID 1 Performance
Read and write performance with RAID 1 depends on a number of factors, including drive speed, controller, cache memory amount, and workload. In some cases, RAID 1 can come close to matching a single disk’s read performance since both drives operate in parallel. However, writes will usually incur a performance hit since data must be written to both disks simultaneously.
Comparing RAID 1 to RAID 0, Raid 0 offers significantly better read and write performance since data is striped across multiple disks. However, RAID 0 provides no redundancy unlike RAID 1. In tests using four 15k RPM SAS drives, RAID 0 achieved up to 900 MB/s sequential reads and writes, while RAID 1 reached 550 MB/s reads but slower 350 MB/s writes [1].
RAID 10 combines aspects of RAID 1 mirroring and RAID 0 striping for both redundancy and increased performance. Benchmarks show RAID 10 outperforming RAID 1 in most tests, providing over double the writes. However, RAID 10 requires a minimum of 4 drives versus just 2 for RAID 1 [2].
Compared to RAID 5, RAID 1 generally provides better read performance but slower writes. RAID 5 write tasks involve parity calculations across multiple disks, limiting its write speeds. But RAID 5 reads can leverage multiple disks for higher throughput than RAID 1’s mirrored disks [3].
RAID 1 in the Cloud
With the rise of cloud computing, many organizations are moving away from traditional on-premises RAID 1 configurations in favor of cloud-based replication for redundancy and availability. Cloud storage providers like Amazon Web Services (AWS) offer mirrored volumes that function similarly to RAID 1 without requiring you to configure it yourself.
For example, AWS Elastic Block Store (EBS) offers the ability to create mirrored volumes for enhanced data durability and availability in case of hardware failure. The mirrored EBS volumes are automatically replicated within a single Availability Zone, protecting your data from the failure of a single component.
Cloud virtual machines (VMs) can also be configured with virtual RAID 1 arrays for data redundancy. However, configuring RAID inside VMs has some downsides compared to using managed mirrored volumes from your cloud provider:
- Requires manual configuration and management of the RAID array
- Does not protect against failure of the entire VM instance
- Less resilient than cloud-native replication between availability zones
Overall, while RAID 1 is still an option for redundancy in cloud VMs, cloud-native replication like EBS mirrors often provides comparable redundancy without the management overhead.
Conclusion
In summary, RAID 1 offers complete data redundancy by mirroring data across multiple disks, ensuring data continues to be accessible even if one disk fails. The key pros are high read performance, complete data redundancy, and simple implementation. The main cons are high disk capacity requirements and reduced write performance compared to single disks.
RAID 1 is an ideal fit for applications where uptime and data redundancy are critical, such as databases, email servers, and other mission-critical systems. The redundancy protects against hardware failure while the performance boost from striping optimizes reads.
When implementing RAID 1, use identical disks from the same manufacturer and batch when possible for optimal performance. Schedule regular disk integrity checks and replace failed disks promptly. Consider adding a hot-spare disk to minimize rebuild times. Use RAID 1 in conjunction with backups for enhanced protection.