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  • What is RAID? – The definitive guide to RAID storage

    Physical drives fail, it’s a fact of life. It doesn’t matter whether it is spinning disks (HDDs) or memory chips (SSDs) that power your server hardware, drive failure is a high risk and you simply won’t get warned.

    Yes, drive failure is less of a risk than it used to be, but the impact of drive failure is no less than it was in the past. Thankfully there is an easy fix in the shape of RAID, albeit a fix that can be costly in terms of storage space.

    Dell EqualLogic PS6110 SAN Array

    What is a RAID drive?

    RAID combines two or more physical drives into one logical RAID drive. RAID is used to both improve disk performance and to protect against disk failure.

    Drives rarely fail simultaneously but it is not uncommon for a single drive in an array to fail. Unfortunately for most workloads the implications of a single drive failing are just about equal to the implication of all drives failing – your server goes down.

    RAID (redundant array of independent disks) relies on the fact that physical drives do not fail simultaneously. By redundantly storing your data in exchange for sacrificing some storage capacity RAID can protect you against individual drive failures.

    How RAID Works

    There are a number of different RAID configurations you can pick from, but all RAID configurations have a common element: RAID stores the same data in multiple places to ensure that the failure of a single drive does not sacrifice the integrity of your data. These are the important characteristics of RAID arrays:

    • Multiple physical drives: A RAID array contains multiple drives by definition. Though a RAID array can contain as few as two physical drives most arrays contain more physical drives to offer a better blend of performance while sacrificing less storage space in achieving redundancy objectives.
    • Firmware controller: Though software, OS-driven raid is entirely possible most RAID configurations will use a hardware controller that manages the RAID array. Drives are attached to a configurable controller which manages the array, redundantly storing data and bypassing failed drives to ensure continued operations.
    • Resistant to drive failure: Except for RAID 0, if a drive fails the RAID controller notifies you of a failure. You then have the opportunity to replace the drive after which the RAID controller will re-build the array, restoring it to full working condition without data loss.
    • Transparency: From the user and operating system perspective a RAID array simply appears like a standard volume. The underlying complexities of the array are invisible, your RAID controller presents an ordinary volume to the operating system while managing the redundancy aspects of the array behind the scenes.

    Important RAID definitions

    Let’s look at a couple of RAID definitions before we discuss the different RAID levels in further detail:

    • Mirroring: At a basic level mirroring involves the exact duplication of data on more than one physical drive to ensure that the failure of one drive does not lead to the failure of the array. Mirroring ensures data is available in more than one place.
    • Striping: RAID striping involves dividing data into blocks that are in turn spread across several disks. Striping improves performance because it allows multiple drives to simultaneously respond to a request, taking advantage of the combined throughput of multiple drives.
    • Parity: RAID parity calculations are used to ensure that data can be fully retrieved from your array even if there is a physical disk failure. Parity data is not an exact copy of data and therefore differs from mirroring. But RAID parity information is sufficient for the reconstruction of data in case of drive failure.
    • Nested RAID: Hybrid or nested RAID levels combine the features of more than one RAID level in an attempt to combine the key advantages of both levels. RAID 10 and RAID 50 are examples of nested RAID.

    Explaining the different RAID levels

    RAID levels refer to the different ways to configure a RAID array. Higher RAID levels are not necessarily better, each level has different advantages in terms of performance and redundancy. There is no right or wrong RAID level, it depends on your use case.

    RAID 0 Striping Diagram

    What is RAID 0?

    This level of RAID is performance-orientated and offers no redundancy. RAID 0 simply makes use of RAID striping to distribute data over two or more disks to boost read and write throughput. You need at least two drives to enable RAID 0, performance increases as you add physical drives.

    • Pros: Performance is the key feature of RAID 0. The lack of a redundancy feature and use of multiple disks means that there is no impediment to pure throughput. Also, RAID 0 does not involve sacrificing any disk space, again because there is no redundancy element.
    • Cons: If one of the drives fail you will suffer the loss of the entire array. In reality RAID 0 increases the risk of data loss because you are doubling up on the probability of failure.
    • What is RAID 0 used for? Pick RAID 0 for non-critical storage where high throughput is crucial, such as video editing. Note that RAID 0 cannot reduce hard drive latency: it only improves throughput, many applications won’t really benefit from RAID 0’s performance advantages.

    RAID 1 Diagram

    What is RAID 1?

    RAID 1 uses drive pairs to create redundancy. For each drive you intend to store data on you need a mirror drive. Thus RAID 1 works with two drives, four drives, ten drives, etc. It is a simple way to ensure redundancy: a full and complete copy of data is duplicated across to another drive via RAID mirroring.

    • Pros: Clearly, the big advantage with RAID 1 is redundancy. If a single drive fails your array will remain operable and you won’t lose data. RAID 1 also offers a performance advantage, read operations are faster but write operations are as with a single drive. Finally, RAID 1 is a very relatively simple technology less prone to data corruption.
    • Cons: With RAID 1 all your data is duplicated 1:1. For this reason, you lose 50% of the storage capacity of your array. Deploy 10 drives with a total capacity of 80TB and you will only find 40TB usable if you apply RAID 1.
    • What is RAID 1 used for? Consider RAID 1 when your storage is absolutely mission-critical, and you want to avoid the risk of a RAID array suffering from corruption. RAID 1 is also more appropriate where absolute storage capacity is not a real concern.

    RAID 5 Diagram

    What is RAID 5?

    RAID 5 ramps up complexity but with complexity come efficiency. Instead of simply mirroring data 1:1 RAID 5 uses parity data to ensure redundancy. You need a minimum of three drives for RAID 5 to operate but you retain more usable storage if you use additional drives.

    A portion of each drive is dedicated to parity data. If a single drive fails the RAID controller can reconstruct the data on the failed drive using the parity data stored on other drives.

    • Pros: The read performance on a RAID 5 array is top-notch and you sacrifice a relatively small amount of disk space to enable redundancy. If a single drive fails your storage array will continue to function.
    • Cons: Write performance can drop as parity calculations are performed while writing. RAID 5 arrays can suffer from substantial performance degradation in case of drive failure. While the array will function, performance will be affected. Restoring the array once you’ve replaced a drive can take a long time due to the underlying complexity of RAID 5.
    • What is RAID 5 used for? RAID 5 offers a good mix of high performance, usable storage plus redundancy and is commonly used in file server applications. However, RAID 5 is not an ideal option when your use-case involves a lot of write operations due to the need to calculate parity information.

    RAID 10 Diagram

    What is RAID 10?

    RAID 5 is a good compromise. An alternative is to combine the advantages of RAID 0 and RAID 1 in one array by using RAID 10. With RAID 10 your RAID controller stripes data across the array of disks while at the same time ensuring data is fully mirrored.

    A nested RAID level, RAID 10 does not calculate parity information. Data is mirrored 1:1, while data is also simultaneously striped.

    • Pros: With RAID 10 you enjoy both high write performance and high read performance as it combines the throughput of multiple drives while avoiding parity calculations. You get full redundancy and should a drive fail your array will suffer less of a performance drop, while rebuilding will be quicker than is the case with RAID 5.
    • Cons: As with RAID 1, you sacrifice 50% of your physical storage capacity when you implement RAID 10. It makes for an expensive way to ensure redundancy once the cost of drives, server equipment, and energy use is all added up.
    • What is RAID 10 used for? Think about RAID 10 if you can afford the number of drives required and absolute storage capacity is not your prime concern. RAID 10 is great for mission-critical workloads that require fast performance.

    Other RAID Levels

    Now that you understand how the commonly-used RAID levels function, including the pros and cons of each, we can look into ways in which you can tweak RAID even further. Depending on your workload one of the following RAID levels may be an even better fit:

    RAID 6 Diagram

    • RAID 6: Similar to RAID 5 but with another layer of parity. With RAID 6 the array is more resilient, RAID 6 can tolerate up to two drive failures. However, you lose more storage space while incurring a further write-speed penalty.
    • RAID 2, 3, 4 and 7: Infrequently used in practice, these RAID levels involve tweaks to the more commonly used RAID levels. For example, RAID 3 is just like RAID 5 with the exception that a single drive is dedicated to storing parity information.
    • RAID 50: Like RAID 10, RAID 50 is a nested RAID level that combines the block-level striping of RAID 0 with the parity capabilities of RAID 5 to ensure a combination of high performance and redundancy. You need at least six drives to enable RAID 50.

    How to setup RAID

    As a concept RAID can apply to a wide range of scenarios. For example, you can set RAID up on a desktop PC as long as it has at least two drives by simply using Windows 10’s built-in software RAID capabilities.

    Most readers will, of course, be interested in setting up RAID in servers and storage devices. Let’s take a look.

    Setting up RAID on your NAS

    One of the benefits of using a NAS for data storage is the fact that your NAS effectively operates as a server. A NAS device includes an on-board computer including a Linux-driven operating system.

    In most cases you do not need to buy additional hardware to enable RAID on a NAS as RAID functionality is part and parcel of NAS capabilities, it is built-in.

    You need to use your NAS operating system to configure RAID on your NAS. Each NAS will have a slightly different process how to RAID, but choosing your RAID level and precise configuration is done during the setup phase.

    RAID on a Dell or HP server

    Your server will include an on-board RAID controller with a configuration utility that you access when the system is booting.

    Dell’s PowerEdge servers, for example, make use of the PERC configuration utility. You need to get into PERC before the server attempts to boot an operating system. This is typically about 20 seconds into the server boot process, the utility is triggered by a keystroke combination – CTRL+R for Dell’s PERC utility.

    Inside the RAID controller’s BIOS utility you can set up your RAID configuration as required. In turn, the RAID controller will present the drives to the operating system as a single volume – or indeed multiple volumes if you configured your RAID setup that way.

    Thinking about how to configure RAID 1 in HP servers? The process will be broadly similar as you still need to access the controller BIOS and configure RAID 1 or another RAID level at that point.

    What does RAID mean for your business?

    Simply put, for businesses that are in physical control of storage and server resources RAID is not optional, it is essential.

    Drive failure can lead to both downtime and permanent data loss. A quick look at annualized hard drive failure rates presents a stern warning: there is a statistically significant chance that a drive will fail in any given year.

    Ensuring your servers and storage kit is configured for RAID means that your business will not be impacted by the failure of a single drive. Yes, configuring RAID incurs costs: for large operations, a 20% reduction in usable storage will have serious cost implications.

    Data loss can be catastrophic, and downtime can play havoc with the ability of your business to continue to generate revenue. RAID protects you against physical drive failure.

    However, RAID is not a backup strategy.

    Can RAID be my backup strategy?

    RAID protects your business against physical disk failure, but it cannot function as your backup strategy. We’ve explained why RAID can protect you against the failure of a single physical disk. Here are just some of the risks RAID cannot protect you against:

    • Physical destruction: Yes, RAID protects you against the failure of a drive, but RAID cannot protect you against natural disasters, nor does it offer protection against fire – a risk that cannot be ruled out. Theft will also override RAID: when an entire device goes missing RAID cannot protect you.
    • Data corruption: Whether it’s ransomware or simply a software fault, data corruption is a risk that RAID offers no protection against.
    • Human error: Unintentional data destruction due to human error is not uncommon and RAID does not offer protection against errors that are committed to an array.

    Clearly, your business still needs to maintain further backups and redundancy processes to ensure that your key customer and business data enjoy adequate protection.

    In summary

    We’ve looked at the benefits of RAID and at the different RAID levels including what each RAID configuration offers. It should be clear by now that RAID is an essential data protection strategy.

    RAID should be implemented by default to protect your business against physical device failure. Yet RAID is not a rounded backup strategy, it serves a single, specific purpose.

    Understanding RAID 5 and other RAID levels and choosing the best RAID option for your use-case can be daunting. Feel free to contact Enterasource for more insight into RAID, including which RAID configuration to use for your requirements.

  • How to Purchase a Server for a Small Business

    Picking a server to meet the needs of a growing business is challenging: there is a wide range of form factors, capacities, and processing power on offer. Here we outline what you need to think about when purchasing a new server for your small to medium-sized business.

    What is the purpose of your server?

    First and foremost, you need clarity on what you plan on using your server for. Businesses are increasingly using cloud services which have eroded the need for traditional server infrastructure for e-mail, SharePoint, and the like. Nonetheless, most businesses still find it beneficial to keep larger files or at least backups on site. For other organizations, regulatory or other requirements may imply that all data, from e-mail through to day to day files, must be kept in-house.
    Management teams may also simply prefer to run their own IT operations, prohibiting cloud use, in which case you will need significant on-site server infrastructure. Careful buying can also arguably save your business money: invest in value-for-money local server infrastructure - and save on cloud license fees. Importantly, the purpose of your server will determine the amount of storage you require, whether virtualization is an important factor, and therefore the processing power you require.

    NAS or full-blown server

    It is worth keeping in mind that sometimes when people refer to an “office server” all they really mean is “office file server” in which case there’s no need to buy a fully functional server running a server OS. If all you need to do is store and share files locally and securely, Network Attached Storage (NAS) will do the job while saving you cash and maintenance hassle. Any more advanced duties such as email, remote access and the like will however require a fully functional server.

    The key server factors you should consider

    Once you’ve established what your rationale is for buying a server you can go ahead and make a few important decisions around the machine itself.

    Physical footprint

    Servers come in two physical configurations: towers, which are freestanding units; and slim-profile rack-mounted servers. A tower server (such as the Dell PowerEdge T620 below) can be placed anywhere in your office that is cool and dry, but finding space for several tower servers can become an issue – these are large computers.

    Dell PowerEdge T620 Tower Server

    Rack-mounted servers need to be mounted in a server rack but are otherwise mostly similar in purpose and function. A single rack is far larger than a single tower server, but racks can accommodate a number of servers in a very tidy space. So, ask yourself: are you going to be using a single server for many years to come, or is your business growing quickly, requiring several servers in the near future? If so, consider buying a rack and a rack-mounted server, the Dell PowerEdge R420 (below) is a typical example.

    Dell PowerEdge R420 Rack Server

    Usage and resource requirements

    There’s no point spending an enormous amount of money on a high-powered machine when the head count for your business is 10 or 20 full-time staff or if the machine will mostly be required to serve files. It is factors such as these that you should take into account when picking the amount of RAM and the number of physical CPUs you require on your machine.
    Also, note that businesses that make extensive use of the cloud could have lower requirements for servers, but your server requirements will be much higher if your business prefers – or is forced to – keep data in-house. Data handled in-house may mean that your employees will need remote access to your server, which will further boost the resource demands on the machine. Finally, all of these requirements added up lead to another factor: virtualization.


    Many readers will be aware of the dramatic effect of virtualization on the way server hardware is procured and deployed. To recap, virtualization allows you to run and manage several server OS instances, all serving a discrete purpose, on a single machine. So, when selecting your server infrastructure you may be better off with a single powerful machine, permitted the necessary protections are in place, compared to several machines serving different duties. Needless to say, virtualization will require plenty of RAM and powerful CPU resources.


    Aside from planning for CPU and RAM requirements, you should also consider storage requirements, now and in the long run. Whether you pick a tower server or a rack-mount unit you will have a choice in the number of drive bays your machine has. Rack units typically also feature different drive bay sizes: if you’re looking for a large amount of cheap storage, make sure you pick a unit with 3.5” bays. If performance is key, pick a unit which features 2.5” bays, ideal for SSDs, such as a HP ProLiant DL360 with 2.5” bays, below.

    HP DL360 G9 SFF


    Finally, servers are intended to be up and running 24/7 with no interruption. However, server components can fail and you should consider buying a server that allows the hot-swapping of these components. The ability to hot-swap hard drives is fairly common, but dual and hot-swappable PSUs (power supply units) – common in rack-mount units – can ensure your server stays up and running around the clock.

    Get in touch with Enterasource for advice

    Buying a server is an important decision for most businesses, not only due to the initial expense involved but also because migrating data from one server to another is hard work. The different options can be overwhelming and we would be glad to assist with any questions you may have. Enterasource can advise you on the right form factor, the amount of RAM you need and your best options around storage and CPU power.

  • Understanding the difference between SAN, NAS and DAS storage

    The differences amongst storage solutions functioning as DAS, NAS and SANs can be tricky to decipher if you are not already familiar with the many ways of provisioning storage. NAS and SANs can be particularly difficult to distinguish.

    Yet when considering a storage solution for your organization a basic understanding of the functionality and best features of each of these three storage options is essential. Once you are invested in a class of storage it can be hard to switch away. Here, we outline the main characteristics of DAS, NAS, and SANs.

    What is Direct Attached Storage (DAS)?

    The simplest to understand, DAS refers to storage which is directly attached to a computer or server. With DAS there are no networking layers between computer and storage. Instead, storage is either internal to the machine or external and directly attached via an interface such as USB or SAS (Serial Attached SCSI). A DAS device could be a single drive, such as a typical external USB drive, or a device which contains bays for several drives. For example, the Dell PowerVault MD1200 (pictured below) carries 120TB of storage, and is directly attached to a server via SAS.

    Some DAS devices also include advanced management functions and comprehensive RAID capabilities. DAS offers the advantage of speed thanks to direct connectivity, but DAS is relatively limited in terms of flexibility – unless the computer it is attached to functions as a file server. Although many IT teams are also concerned about the single point of failure presented by DAS, DAS is a good option for use by a single user, or for small user groups.

    What is Network Attached Storage (NAS)?

    A NAS device is effectively a fully functional computer, with copious storage capacity, attached to your internal network. NAS devices include an operating system and a single drive bay or several drive bays, many NAS units can accommodate large numbers of drives in advanced RAID configurations. NAS devices are dedicated to serving files and the hardware and OS involved is fine-tuned to offer excellent reliability, an advantage over a file server + DAS combination.

    NAS storage

    Though NAS offers solid flexibility it does have a limitation in that data cannot be accessed at the block level as with DAS or SANs. To access data on a NAS your team members need to add the network storage location as a file share. This is fine for many use cases, such as file sharing, but will limit progress under other scenarios. In contrast, DAS and SAN solutions allow you to access storage as if it is internal to a machine.

    What is a Storage Area Network (SAN)?

    SANs are similar to NAS in some ways but offer far more advanced features which increase the flexibility of the underlying storage. The main difference lies in that SAN configurations allow block-level access, which NAS does not. Benefits include increased speed and the ability to, for example, boot an operating system across the network. In addition, thanks to block-level access, storage areas on a SAN can appear as internal drives on a machine.

    As much as SANs offer more advanced features, SANs introduce complexity which can overshadow the benefits. Though you start off with a multi-bay device such as the Dell EqualLogic range (pictured below), a working SAN configuration requires a range of additional infrastructure components including SAN switches, disk controllers, host bus adapters and the connecting fiber cables. It also requires intelligent network management, and SANs are not easy to configure.

    Dell EqualLogic SAN

    Choosing the right storage option

    Your storage solution of choice will depend on the size of your team, the amount of networking skills you have available in your team and the applications which your organization will use. Only by taking into account all three these factors will you be able to choose between the advantages and drawbacks of each option. Foresight is also an important factor: whichever solution you choose must scale with your growing requirements for a reasonable period of time.




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