What is RAID?
RAID stands for Redundant Array of Independent Disks. It is a data storage technology that combines multiple physical disk drives into one or more logical units to improve performance, redundancy, or both.
There are several levels of RAID that work differently:
- RAID 0 stripes data across multiple disks for improved performance, but provides no redundancy.
- RAID 1 mirrors data across disks for redundancy, at the cost of halved storage capacity.
- RAID 5 distributes parity information across disks, providing redundancy with better storage efficiency than mirroring.
- RAID 10 combines mirroring and striping for both performance and redundancy.
The main purposes of RAID are to increase performance, provide fault tolerance through redundancy, or deliver both benefits. By grouping multiple physical disks together, RAID can improve speed for reads and writes. It also allows continuous operation if one disk fails by reconstructing data from the remaining disks.
Overall, RAID aims to enhance storage performance, reliability and capacity by coordinating how data is physically arranged and accessed across an array of independent disks.
RAID 0
RAID 0, also called disk striping, splits data evenly across two or more disks without parity information. This RAID level increases performance by spreading the load across multiple disks, allowing for simultaneous read and write operations. However, RAID 0 provides no redundancy – if one disk fails, all data will be lost. Since there is no parity data, the storage capacity in a RAID 0 array is the sum of all the disks.
According to TechTarget, “RAID 0 does not use data redundancy, so the failure of any physical drive in the striped disk set results in the loss of the data on the striped unit.” While RAID 0 improves speed, it comes at the cost of fault tolerance. For this reason, RAID 0 is generally used in non-critical storage environments where performance is paramount and data backup exists elsewhere.
RAID 1
RAID 1, also called disk mirroring, copies data identically to two or more disks (at least 2 disks). This level provides redundancy but no performance gain. With RAID 1, data is written identically to two or more drives simultaneously (Source: https://www.techtarget.com/searchstorage/definition/disk-mirroring). If one drive fails, the data can still be accessed from the other mirrored drive(s) as there are duplicates of the data. However, RAID 1 does not improve disk I/O performance compared to a single disk. The write performance is worse than a single disk, as every write operation has to be performed on every disk in the array (Source: https://www.source-data.com/resources/what-is-the-difference-between-raid-and-mirroring/).
RAID 5
RAID 5 stripes data across multiple disks with parity information distributed across the disks (techtarget.com). This parity allows for redundancy in case a single disk fails. By striping data across multiple disks, RAID 5 provides increased performance over a single disk.
With RAID 5, a minimum of 3 disks is required. Data is split and written across the disks in chunks called stripes. Parity information is calculated and written across the stripes. If a single disk fails, the parity information can be used to reconstruct the lost data from that disk (promax.com). This provides redundancy and protection against data loss.
Because the data is striped across multiple disks, RAID 5 provides increased performance over a single disk. The parity calculation does incur some processing overhead, but overall RAID 5 offers improved performance compared to mirrored or non-RAID disk configurations.
In summary, RAID 5 stripes data across disks with parity distributed across disks. This provides redundancy to protect against disk failure while also increasing performance over a single disk.
RAID 10
RAID 10, also known as RAID 1+0, combines both mirroring and striping to provide increased performance as well as redundancy (cite url1). In RAID 10, data is mirrored and then the mirrors are striped. This means there are two copies of each data set that are then split and distributed across multiple drives (cite url2).
The mirroring in RAID 10 provides redundancy. If one drive in the mirror set fails, the data can still be accessed from the other mirrored drive. The striping increases performance by allowing reads and writes to multiple drives at once (cite url3).
RAID 10 requires at least 4 drives to implement. It provides good performance for applications that demand faster disk access and also need redundancy to protect against disk failures (cite url1). The tradeoff is that RAID 10 has lower storage efficiency since data is duplicated through mirroring.
Choosing a RAID Level
When selecting a RAID level, there are several key factors to consider such as performance needs, redundancy requirements, and cost:
RAID 0 is best suited for performance-intensive applications where redundancy is not critical. By striping data across multiple drives with no parity, RAID 0 enables faster reads and writes. However, it offers no fault tolerance since if one drive fails, all data will be lost (Source).
RAID 1 is ideal for critical data that needs to be protected through drive mirroring. It provides complete data redundancy by duplicating information on a secondary drive, but at the cost of requiring double the storage capacity (Source).
RAID 5 offers a balance of performance and redundancy by striping data across drives with distributed parity information. If a single drive fails, data can be rebuilt using the parity drive. However, write performance suffers due to parity calculation overhead (Source).
RAID 10 combines mirroring and striping for increased performance and redundancy. By mirroring striped sets, RAID 10 can withstand multiple drive failures with minimal performance impact. However, it requires at least four drives and 50% storage overhead (Source).
Implementing RAID
There are two main methods for implementing RAID: hardware RAID and software RAID. With hardware RAID, a dedicated RAID controller card is used to manage the RAID array. The controller has its own processor, cache, and firmware that handles the RAID calculations and data distribution (https://www.techtarget.com/searchstorage/tip/Key-differences-in-software-RAID-vs-hardware-RAID). Hardware RAID generally offers better performance than software RAID, but the RAID controller card adds additional cost.
With software RAID, the RAID calculations and data distribution are handled by the operating system and drivers. This allows the RAID array to be set up using the existing hardware components without any additional cost for a hardware controller. However, software RAID utilizes system resources like CPU, RAM, and bus, which can potentially impact performance (https://www.reddit.com/r/DataHoarder/comments/106b9jh/hardware_raid_vs_software_raid/).
Setting up a RAID array involves configuring the RAID level and drives through the RAID controller interface or software RAID management utility. Most RAID implementations include tools to monitor and manage the RAID array, check drive status, rebuild failed drives, and perform other administrative tasks. Regardless of hardware or software RAID, proper configuration is required for the desired performance and redundancy characteristics.
RAID Performance
RAID performance varies greatly depending on the RAID level used. Synthetic benchmarks show that RAID levels that stripe data across multiple disks, such as RAID 0, RAID 5, RAID 10 and RAID 50, can provide significant performance improvements compared to using just a single disk drive [1]. However, the performance gains depend on the number of disk drives used in the array.
In general, RAID 0 provides the fastest performance but no redundancy. RAID 1 and RAID 5 provide moderate performance improvements. RAID 10 combines mirroring and striping to achieve excellent performance that scales linearly with the number of drives. However, RAID 10 is costly since it requires at least 4 drives.
Choosing the right RAID level requires balancing performance, redundancy, and cost for the particular application. Enterprise and mission critical systems often use RAID 10 or RAID 50 to maximize both performance and redundancy.
RAID and Redundancy
One of the key benefits of RAID is that it protects against disk failures by providing redundancy. RAID levels like RAID 1, 5, and 10 use data mirroring or parity to allow continued operation if one drive fails. This prevents data loss and downtime in the event of a drive failure.
When a drive does fail in a redundant RAID array, the array can be rebuilt using the remaining disks. For RAID 1, the mirror drive can continue operating while the failed drive is replaced. Then the RAID is resynchronized to recreate the mirror. For RAID 5, the parity information is used to recalculate the data that was on the failed drive and restore redundancy. This rebuild process allows restoring the array without data loss [1].
To make rebuilding easier and faster, many RAID controllers also support hot spare drives. These are extra drives provisioned for the RAID that are unused until a failure occurs. When a disk fails, the hot spare is automatically swapped in to start the rebuild process. This avoids the need to physically replace the disk first. Hot spares can significantly reduce downtime after a disk failure [2].
Conclusion
In summary, RAID levels allow you to configure multiple hard drives to optimize for performance, redundancy, or both. RAID 0 stripes data across multiple disks with no parity or mirroring, improving speed but providing no fault tolerance. RAID 1 mirrors drives to provide redundancy at the cost of storage capacity. RAID 5 distributes parity information across drives, delivering faster speeds than RAID 1 while still providing redundancy. RAID 10 combines mirroring and striping for faster performance with redundancy.
When it comes to performance without redundancy, RAID 0 is the clear choice. By striping data across multiple disks with no parity or mirroring, RAID 0 provides improved speed for reads and writes. However, if any one disk fails, all data will be lost. The tradeoff for performance gains is complete lack of fault tolerance.
Other RAID levels like 1, 5, and 10 offer various balances of redundancy and performance. When choosing a RAID level, consider your performance and redundancy needs. RAID 0 provides speed at the cost of protection. The other RAID levels offer redundancy and can optimize performance through techniques like disk striping.