Why use RAID 5 instead of RAID 1?

When configuring storage for a server, one of the most important decisions is which RAID level to use. RAID 1 and RAID 5 are two popular options, but they have key differences in how they store and protect data. RAID 1 creates an exact copy (mirror) of data on a second drive, while RAID 5 stripes data across multiple drives with parity information that allows for one drive failure without data loss. There are pros and cons to both, but RAID 5 tends to be preferable for many use cases because it offers greater storage efficiency and allows systems to continue operating optimally after a single drive failure. Let’s explore the key factors in more detail.

Storage Efficiency

One of the biggest advantages of RAID 5 over RAID 1 is more efficient use of storage capacity. With RAID 1, the total usable space is equal to the capacity of one drive, because a full copy of all data is written to the second mirrored drive. This means 50% of total capacity is used just for redundancy. In contrast, RAID 5 gets significantly better efficiency by striping data across multiple drives. The equivalent of one drive’s worth of space is used for parity information rather than a full copy, so you get 80% or more of total capacity as usable space. The more drives in the RAID 5 array, the closer usable space gets to total capacity.

For example, four 2TB drives in RAID 1 would give you 2TB total usable space. The same four 2TB drives in RAID 5 would provide about 6TB of usable space. With eight 2TB drives, RAID 1 would still only give 2TB space while RAID 5 would offer around 14TB. As server storage needs continue growing, the superior efficiency of RAID 5 becomes increasingly beneficial compared to the rigid 50% overhead of RAID 1.

Drive Failure Resilience

The other area where RAID 5 pulls ahead of RAID 1 is how well it handles drive failures. Both offer protection against data loss from a single drive failure. However, with RAID 1, the failed drive must be replaced immediately to restore full redundancy. If a second drive fails before that, complete data loss can occur. RAID 5 arrays can continue operating optimally after a single drive failure by using the parity information to rebuild the missing data. A replacement drive can be installed at a later convenient time. Thanks to this flexibility, RAID 5 offers greater resilience against data loss from drive failures.

RAID 5 arrays with larger drive counts can even withstand multiple drive failures under certain circumstances. For example, a RAID 5 array with eight drives could operate in a degraded state with up to two failed drives if the failed drives are not next to each other. The remaining drives could still be read parallelly to access all data. Overall, RAID 5 provides superior redundancy and fault tolerance compared to RAID 1 when using larger drive counts.


In terms of performance, RAID 5 can often outpace RAID 1 despite the parity calculation overhead. By striping data across multiple drives, RAID 5 can process multiple I/O requests simultaneously. Most RAID 5 implementations use dedicated parity drives to further reduce the performance impact of parity calculations. RAID 1 lacks parallelism because data is mirrored on a second isolated drive. All reads need to come from the first data drive. Writes also lack parallelism because every write must go to both the data drive and its mirror. For use cases that demand higher throughput, RAID 5 is usually the better performing choice.

Read Performance

For predominantly read-heavy workloads, RAID 5 offers significantly better performance scaling than RAID 1. With more drives added to a RAID 5 array, read operations can be parallelized across more drives simultaneously. RAID 1 can’t improve read performance by adding more mirrored drives. The server can only read from one drive in each mirrored pair at a time. As server processors get more cores, RAID 5 is better positioned to take advantage of parallelism improvements.

Write Performance

RAID 5 write performance is also superior due to its drive parallelism. Writes only require updating the data drive and parity drive for a stripe, not every drive like with RAID 1 mirroring. However, RAID 5 does have higher write latency due to the parity calculation. Using a dedicated parity drive mitigates this issue at the expense of usable capacity. For predominantly write-heavy workflows, benchmarking different RAID 5 configurations can determine optimal performance.

RAID 1 can have better resynchronization performance after a drive failure since it only needs to copy from a mirror drive rather than rebuild from parity. But in normal operating conditions, RAID 5 generally delivers faster writes.

Cost Effectiveness

RAID 5 is usually a more cost-effective solution compared to RAID 1. Because it uses storage capacity far more efficiently, you need significantly less raw storage to achieve the same usable capacity. Not only can this reduce your upfront storage hardware costs, but it also saves on power, cooling, and rack space needed to store the extra drives required in a RAID 1 array. These savings multiply as your storage needs grow over time.

RAID 5 also allows incremental expansion. You can increase capacity as needed by adding more drives to the array. With RAID 1, expansions typically require adding full mirrored pairs of drives. The flexible scalability of RAID 5 can let you better align storage costs with actual business needs.

Use Cases

Given its advantages, RAID 5 tends to be a better option than RAID 1 in most server storage use cases including:

  • File servers and NAS appliances storing large amounts of business data, media files, backups, etc.
  • Database servers that demand higher capacity and throughput.
  • Web and application servers that require good read performance.
  • Video surveillance storage needing 24/7 operation after drive failures.

The performance and capacity improvements of RAID 5 make it ideal for general-purpose storage. RAID 1 can still be a good fit for smaller storage needs that demand the better write performance and simplicity of mirroring.

RAID 1 Use Cases

Here are some examples where RAID 1 may be preferable to RAID 5:

  • Smaller servers that only need a few terabytes of storage.
  • Boot drives where faster writes are critical and capacity is secondary.
  • Low-end NAS devices focused on data protection rather than performance.
  • Any environment where simplicity and ease of management is a priority.


While both RAID 1 and RAID 5 offer data protection through drive redundancy, RAID 5 is typically the superior choice for most server storage needs. By striping data across drives, RAID 5 provides excellent storage efficiency, faster read/write performance, drive failure resilience, and flexible scalability. Outside of smaller deployments where simplicity and mirroring may be preferable, RAID 5 is usually the best option for optimizing capacity, throughput, and cost-effectiveness.

Migrating from RAID 1 to RAID 5 can deliver significant advantages as storage needs grow. With careful planning and preparation, the migration process can minimize downtime and disruption. When configured properly, RAID 5 arrays can continue serving data without issues after the changeover. For organizations wanting to scale server storage efficiently while maximizing protection against drive failures, moving from RAID 1 to RAID 5 is a logical step forward.