Storing data is one of the fundamental uses of a computer system. There are multiple kinds of storage solutions available, and each one of them has different advantages and use-cases. Solutions like Hard Disk Drives (HDD) are a cheap yet primitive alternative, while those like Solid State Drives (SSD) are fast, reliable but expensive. However, there is another alternative that balances efficiency and cost to present the perfect choice for small enterprises — RAID.
Redundant Array of Independent Disks (RAID) is a way of putting multiple physical disk drives into a logical array to provide optimized data protection, system performance, and storage space. When put together, these small disks act as one powerful, expensive disk. The RAID technology is composed of multiple levels, and each level offers a trade-off between the target features — data protection, storage space, and system performance.
In this article, we will take a look at what RAID Storage is, how it is different from the traditional storage method, and where to use it. Before getting started with all this, let’s first understand the various levels of RAID Storages available.
What is RAID Storage?
RAID is a concept of putting together multiple inexpensive disks to imitate a more expensive, powerful disk that can tolerate hardware failure as well. In situations where enhanced data reliability or faster access is needed, RAID storage fares better than the conventional single-disk based storage solutions. The disks that make up a RAID storage setup can be arranged in various ways. These arrangements are called levels, and each level focuses on providing situation-specific advantages like better reliability, faster read, and increased robustness.
Levels of RAID Storage
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While there are several levels in RAID, not all of them are in practical use. Levels like three and four are intermediate to more popular levels like five and six. Following are some of the most common levels of RAID Storage:
RAID 0 (Striping)
This level distributes data across a large array of disks, which provides great access speeds. These greater access speeds are available because the data can now be stored and read from multiple disks at once. But there is no data redundancy at this level, meaning that no duplicates of the data stored are available. This further means that if there is a failure in any of the disks, it will result in complete data loss.
RAID 0 is rarely used in a production environment. It finds its use in cases like caching, where data loss does is less important, but speed is of top priority.
RAID 1 (Mirroring)
RAID 1 builds upon the concept introduced in RAID 0 but adds a layer of duplicity in the data stored. This means that all the data stored across a RAID 1 storage is stored two times, and is not lost as long as one copy is intact. RAID 1 focuses completely on data reliability.
RAID 1 also offers increased read performance, as the same data can now be found in any of the two copies. However, this introduces a delay when writing the data, as it has to be written on two disks.
RAID 5 (Striping with Single Parity)
RAID 5 builds upon the idea of RAID 0 to store data in strips across multiple drives. It adds parity information to the data, and thus it requires at least three drives to build a RAID 5 system. This parity information, which is distributed across the drives, can help in regenerating data if one of the drives fails. Parity refers to a checksum calculated using all bits in a data sample. This checksum helps to determine if a data loss has occurred in the database, and this same information can also be used to regenerate the lost bits.
RAID 5 brings significant read performance, like RAID 0. But write performance depends on the RAID controller used, as each controller calculates and stores parity information in its own, unique ways. A RAID controller is a device that manages the physical disk drives and connects them to the computer as logical units.
RAID 5 is a good option for web servers, file servers, and other systems where read operations are more frequent. RAID 5 is not suitable for a write-heavy environment.
RAID 6 (Striping with Dual Parity)
RAID 6, similar to RAID 5, builds upon the idea of RAID 0 and strips data across multiple disk drives. RAID 6 stores dual parity information with data and thus it requires two additional disk drives, increasing the minimum number of drives needed to four. Dual parity information can help regenerate data faster than single parity information.
RAID 6 offers improved read performance over Raid 5. But write performance and setup costs for RAID 6 are worse than RAID 5, as you need to add an additional disk drive. Dual parity calculations can be more time consuming than single parity calculations while writing. RAID 6, too, is a good alternative for traditional web servers, file servers, and other read-heavy environments, but it does not fare well in write-heavy use-cases, like social media platforms, and public service portals.
RAID 10 (Striping with Mirroring)
RAID 10 works with a minimum of four disk drives and is a combination of RAID 1 (mirroring) and RAID 0 (striping). RAID 10 offers both speed and redundancy of data. This is usually the optimal level to use in scenarios where you need high-speed access, but reliability also at the same time.
In a four-drive, minimum configuration, two mirrored drives hold one-half of the striped data while the other two mirrored drives store the other half. This provides you with the flexibility to regenerate your entire data from just two of the four drives. This is similar to RAID 1 in terms of storage size and read/write performance.
Advantages of Using RAID Storage
While RAID storage requires additional set-up before use, there are benefits. Let’s take a look at some of them:
RAID storage helps emulate expensive, powerful disks by using multiple smaller, inexpensive disks. This reduces infrastructure costs by a great magnitude. This is especially beneficial for smaller enterprises that can not afford to set up a huge infrastructure.
With the additional number of disks, as well as special access methods defined, most RAID levels gain performance benefits in either reading or writing data. This increased performance directly relates to increased revenue for business use cases, as the system can now handle more requests than usual.
Since data is stored in multiple copies, failure of one of the copies does not mean access to the data is lost. The system can still channel all requests to the functioning disk drive while the faulty drive is replaced and data is regenerated.
Since the data is stored in multiple copies in any RAID level except 0, it is easy to regenerate the lost data in case of infrastructure failures. This makes the system more robust, and data more reliable in the application.
Issues with RAID Storage
Although RAID storage offers many benefits over normal single-disk storage, they also have a few downsides. Following are the most common problems faced when using RAID storage:
Complex RAID Levels are Expensive
Simple RAID levels like RAID 0 through 6 can be built easily with small, cheap disks. But complex levels like RAID 10 require an additional number of disks as well as special hardware like complex controllers to moderate data, read and write. This set-up can be more expensive than the standard RAID set-up.
Data Failure can Happen Across All Drives
RAID relies on the concept of at least one copy of the data to be functioning, to regenerate. However, it is very likely that due to the uniform aging of all drives, they may fail at once. This leaves the system with no reliable backup to fall back to.
Rebuilding is Time-consuming
Rebuilding failed drives requires replacing the drive manually and then regenerating the data which was present on it. While rebuilding is easy for simple levels like 0 and 1, the process becomes complex for advanced levels like 5 or 6, which require processing and operating data to produce meta information like parity.
When a Disk Drive Fails, Others are Vulnerable
Disk drives in RAID rely on each other to maintain redundancy and robustness. If a drive fails, the working drive, most probably, does not have an active backup to fall back to. This means that if a second drive fails while the first failed drive is being replaced, a complete data loss can occur. This can be countered by monitoring the status of all drives, backing up data and replacing the disks before they fail.
Where is RAID Storage Used?
Understanding where the various aspects of Raid Storages allows you to see how they are used. Here are some of the top use-cases of RAID Storages:
When high uptime is required
Systems like RAID are extremely useful to businesses for which uptime and availability are important. Regular backups can help you restore breaking data losses, but they can take days to complete.
In real-life scenarios, any amount of downtime directly equates to lost business. Apart from that, organizations enter into legal agreements with their clients/customers to provide a certain level of availability. A system like RAID ensures the data is available to your application while a failed disk is being replaced.
When high performance is needed
RAID storage systems incorporate stripped-down, duplicate copies of data. This means the same data can be accessed by multiple clients at once. So, applications that face a high volume of database access can benefit from RAID storages to allow greater bandwidth of data access.
When faster reads/writes are needed
Apart from supporting high volumes of access, RAID also facilitates faster speeds in reading and writing files. As data is available across multiple disks, parts of it can be read in parallel simultaneously to facilitate faster reads.
The Future of RAID
The concept of RAID has been around since 1987, but it is still widely used in the computing industry for creating reliable and high-performance data stores.
Very recently, RAID has been observing a decrease in usage, with emerging technologies like erasure coding and SSDs. The primary issue with RAID is with an increasing volume of disks, the chances of failure increase too, and the industry has been observing an exponential increase in disk capacities lately.
The RAID technology seems just perfect for contemporary storage needs. With the added benefits of better reliability, improved performance, and enhanced bandwidth of access, RAID offers an unmatched experience compared to other hard disk drives at the same level. Even though the industry is shifting towards solutions that can fare better for huge disk capacities, RAID still is the primary player in the field of data storage for now.
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