RAID Array Failures & Recovery

RAID Arrays Failures & RecoveryA hardware RAID implementation requires at minimum a RAID controller. On a desktop system this may be a PCI expansion card, PCI Express expansion card or built into the motherboard. Controllers supporting most types of drives may be used – IDE/ATA, SATA, SCSI, SSA, Fibre Channel, sometimes even a combination. The controller and disks may be in a stand-alone disk enclosure, rather than inside a computer. The enclosure may be directly attached to a computer, or connected via SAN. The controller hardware handles drive management and performs any parity calculations required by the chosen RAID level.

Hardware RAID Failures:

  • Actuator Failure
  • Bad sectors
  • Controller Failure
  • Controller Malfunction
  • Corrupted RAID
  • Lightning, Flood and Fire Damage
  • Damaged Motor
  • Drive physical abuse
  • Hard disk component failure and crashes
  • Hard disk drive component failure
  • Hard drive crashes
  • Hard drive failure
  • Head Crash
  • Intermittent drive failure
  • Media Damage
  • Media surface contamination
  • Multiple drive failure
  • Power Spike
  • Power Supply Burn out or failure
  • RAID controller failure
  • RAID corruption
  • RAID disk failure
  • RAID disk overheat
  • RAID drive incompatibility
  • RAID drive overheat
  • RAID Array failed
  • Vibration damage

Hardware RAID Failures(Human Error):

  • Unintended deletion of files
  • Reformatting of drives / Array
  • Reformatting of partitions
  • Incorrect replacement of media components
  • Accidentally deleted records
  • Mistaken overwritten database files
  • Employee sabotage
  • Lost/Forgotten password
  • Overwritten files
  • Overwritten RAID config files
  • Overwritten RAID settings
  • RAID incorrect setup
  • RAID user error

Software RAID implementations are now provided by many operating systems. Software RAID can be implemented as:

  • layer that abstracts multiple devices, thereby providing a single virtual device (e.g. Linux’s md).
  • a more generic logical volume manager (provided with most server-class operating systems, e.g. Veritas or LVM).
  • component of the file system (e.g. ZFS or Btrfs).

Software RAID Failures:

  • Back up failures
  • Computer virus and worm damage
  • Corrupt files / data
  • Damaged files or folders
  • Directory corruption
  • Firmware corruption
  • Repartition
  • Server registry configuration
  • Missing partitions
  • RAID configuration
  • Reformatting

Software RAID Failures(Application Failure)

  • Applications that are unable to run or load files
  • Corrupted files
  • Corrupted database files
  • Data corrupted
  • Locked databases preventing access
  • Deleted tables

About RAID Data Recovery

The majority of Small-to-Medium Enterprises across the globe have turned to RAID-configured systems for their storage solutions. The most frequently cited reasons for utilizing RAID Arrays in businesses today are the highly fault-tolerant level the solution offers and the cost effectiveness of acquisition and maintenance.

However, if a RAID Array does fail due to component malfunctions (including hard drives and controller cards) or operating and application corruption, it leaves the data unusable and in most cases corrupted.

RAID data recovery is an intricate task since RAID data configurations are often custom-built applications developed by competing manufacturers. Without in-depth knowledge of how RAID arrays are configured at both a hardware, firmware and software level, data recovery attempts will not only fail, but result in further data corruption.

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RAID Controller Cards

  • HighPoint Technologies
    Manufacturer of IDE and IDE-RAID controllers.
    www.highpoint-tech.com
  • ICP vortex
    Manufacturer of PCI-SCSI and PCI-Fibre Channel RAID disk array controllers.
    www.icp-vortex.com
  • Conduant Corporation
    Designs and manufactures digital disk-based data recording, FIFO, CPCI, and IDE RAID controller systems.
    www.conduant.com
  • Perceptive Solutions, Inc.
    Manufactures high performance RAID and caching disk controllers for SCSI and IDE.
    www.psidisk.com

To add your RAID Controller Cards here, please feel free to contact us!

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RAID Systems Manufacturers

  • Promise Technology, Inc.
    Designs and manufactures storage solutions using ATA/Serial ATA technology for fast, reliable data protection.
    www.promise.com
  • 3ware, Inc.
    Provides high-performance, scalable RAID storage solutions based on 3ware’s switched architecture.
    www.3ware.com
  • Ciprico, Inc.
    Designs, manufactures, markets, and services RAID disk arrays for high-performance imaging and digital media applications worldwide.
    www.ciprico.com
  • RAIDmax
    High performance RAID Systems by Netsource.
    www.raidmax.com
  • Arco Computer Products, Inc.
    Developing IDE disk mirroring solutions.
    www.arcoide.com
  • Storage Computer
    Provider of high-performance storage and data delivery systems.
    www.storage.com
  • Medéa Corporation
    Manufacturer of the VideoRaid family of disk arrays.
    www.medea.com
  • nStor
    Developer of storage-network based products and services.
    www.nstor.com
  • Advanced Computer & Network Corporation
    Designs, manufactures, and markets data storage RAID systems.
    www.acnc.com
  • Eurologic Systems Ltd
    RAID and storage arrays for the open systems market (HPUX,AIX,Digital UNIX, SunOS, Solaris, OpenVMS, NT, IRIX, Novell, etc.)
    www.eurologic.com
  • Open Storage Solutions
    www.openstore.com
  • RAID, Inc.
    Manufacturer of high performance RAID arrays backed by 24-hour service and support.
    www.raidinc.com
  • Bering Technology, Inc.
    Manufactures disk and tape storage solutions for HP computers.
    www.bering.com
  • Storage Engine
    Supplies products that store, protect, and manage data in complex networks.
    www.storageengine.com
  • Integrated Archive Systems, Inc.
    Provider of high availability and enterprise storage management solutions for UNIX and NT environments.
    www.iarchive.com
  • Inline Corporation
    www.inlinecorp.com
  • Zzyzx Peripherals
    Specializes in disk, tape backup, and network storage for Unix, Linux, Windows, and Netware environments.
    www.zzyzx.com
  • RAID Web [SPONSOR]
    High performance Arena RAID systems using inexpensive IDE and SCSI drives. Works with all operating systems. Division of Electronix Corporation.
    www.raidweb.com
  • Adjile Systems
    Manufacturing SCSI enclosures and RAID solutions. We can supply bare enclosure or fully integrated RAID Systems.
    www.adjile.com
  • MaxTronic International Co., Ltd
    Manufactures and distributes high-performance RAID solutions.
    www.maxtronic.com
  • Caen Engineering
    Manufacturer of custom design housing for SCSI hard disks, RAID enclosures, controllers and mass data storage devices specifically for the reseller and OEM.
    www.caeneng.com
  • Synetic Inc.
    Provides RAID products and solutions for businesses and systems professionals.
    www.synetic.net
  • Fibrenetix Storage Ltd
    Develops, manufactures, and supports the Zero-D range of high performance RAID products.
    www.zero-d.com
  • DataStor
    Offers external RAID and mass storage enclosure cabinets to house SCSI peripherals.
    www.dstor.com
  • RAIDking Technologies
    Offers modular, scalable, fault-tolerant RAID-based storage products.
    www.raidking.com
  • Storage Apps
    Provider of enterprise storage infrastructure products.
    www.storageapps.com
  • Dynamic Network Factory, Inc.
    Provider of network-attached storage and RAID systems.
    www.RAIDexpert.com
  • Conley
    High performance RAID storage management solutions for UNIX, NT and Macintosh platforms. Products include RAID subsystems and RAID related software.
    www.conley.com
  • MacRAID
    Offers the latest in data storage solutions for Mac Users. By RAIDking Technologies.
    www.macraid.com
  • Media Integration, Inc.
    Specializing in custom integration and support for SCSI and fibre channel RAID systems, DLT autoloaders and libraries, and servers.
    www.mediainc.com
  • Storagepath
    Specializing in high performance backplane enclosure systems for SCSI and RAID systems.
    www.storagepath.com
  • Kersey Tech, Inc
    Hot swappable and N+1 redundant power source for raid enclosures, and other RAID related products.
    www.kerseytech.com
  • IFT Europe Ltd.
    Manufactures RAID mass storage subsystems.
    www.iftraid.com
  • Accusys
    Manufacturer of high performance RAID controllers based on IDE/UltraDMA, SCSI, and Fibre channel technologies.
    www.accusysraid.com
  • Accordance Systems
    offers IDE-IDE Raid products.
    accordance.com.tw

To add your RAID System Manufactures Link here, please feel free to contact us!

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RAID 6 — Do you really like it?

RAID 6For several years now RAID 5 has been one of the most popular RAID implementations. Just about every vendor that supplies storage to enterprise data centers offers it, and in many cases it has become — deservedly – a well-trusted tool. RAID 5 stripes parity and blocks of data across all disks in the RAID set. Even though users now must devote about 20% of their disk space to the parity stripe, and even though read performance for large blocks may be somewhat diminished and writes may be slower due to the calculations associated with the parity data, few managers have questioned RAID 5’s usefulness.

There are however, two major drawbacks associated with using RAID 5. First, while it offers good data protection because it stripes parity information across all the discs within the RAID set, it also suffers hugely from the fact that should a single disc within the RAID set fail for any reason, the entire array becomes vulnerable — lose a second disc before the first has been repaired and you lose all your data, irretrievably.

This leads directly to the second problem. Because RAID 5 offers no protection whatsoever once the first disc has died, IT managers using that technology have faced a classic Hobson’s choice when they lose a disc in their array. The choices are these. Do they take the system off-line, making the data unavailable to the processes that require it? Do they rebuild the faulty drive while the disc is still online, imposing a painful performance hit on the processes that access it? Or, do they take a chance, hold their breath, and leave the drive in production until things slow down during the third shift when they can bring the system down and rebuild it without impacting too many users?

This choice, however, is not the problem, but the problem’s symptom.

The parity calculations for RAID 5 are quite sophisticated and time consuming, and they must be completely redone when a disk is rebuilt. But it’s not the sophistication of all that math that drags out the process, but the fact that when the disk is rebuilt, parity calculations must be made for every block on the disk, whether or not those blocks actually contained data before the problem occurred. In every sense, the disk is rebuilt from scratch.

An unfortunate and very dirty fact of life about RAID 5 is that if a RAID set contains, say, a billion sectors spread over the array, the demise of even a single sector means the whole array must be rebuilt. This wasn’t much of a problem when disks were a few gigabytes in size. Obviously though, as disks get bigger more blocks must be accounted for and more calculations will be required. Unfortunately, using present technology RAID recovery speed is going to be constant irrespective of drive size, which means that rebuilds will get slower as drives get larger. Already that problem is becoming acute. With half-terabyte disks becoming increasingly common in the data center, and with the expected general availability of terabyte-sized disks this fall, the dilemma will only get worse.

The solution offered by most vendors is RAID 6.

The vendors would have you believe that RAID 6 is like RAID 5 on steroids: it eliminates RAID 5’s major drawback – the inability to survive a second disk failure – by providing a second parity stripe. Using steroids of course comes with its own set of problems.

RAID 6 gives us a second parity stripe. The purpose of doing all of the extra math to support this dual parity is that the second parity stripe operates as a “redundancy” or high availability calculation, ensuring that even if the parity data on the bad disk is lost, the second parity stripe will be there to ensure the integrity of the RAID set. There can be no question that this works. Buyers should, however, question whether or not this added safety is worth the price.

Consider three issues. RAID 6 offers significant added protection, but let’s also understand how it does what it does, and what the consequences are. RAID 6’s parity calculations are entirely separate from the ones done for the RAID 5 stripe, and go on simultaneously with the RAID 5 parity calculations. This calculation does not protect the original parity stripe, but rather, creates a new one. It does nothing to protect against first disk failure.

Because calculations for this RAID 6 parity stripe are more complicated than are those for RAID 5, the workload for the processor on the RAID controller is actually somewhat more than double. How much of a problem that turns out to be will depend on the site and performance demands of the application being supported. In some cases the performance hit will be something sites will live with, however grudgingly. In other cases, the tolerance for slower write operations will be a lot lower. Buyers must balance the increased protection against the penalty of decreased performance.

Issue two has to do with the nature of RAID 5 and RAID 6 failures.

The most frequent cause of a RAID 5 failure is that a second disk in the RAID set fails during reconstruction of a failed drive. Most typically this will be due to either media error, device error, or operator error during the reconstruction – should that happen, the entire reconstruction fails. With RAID 6, after the first device fails the device is running as a RAID 5, deferring but not removing the problems associated with RAID 5. When it is time to do the rebuild, all the RAID 5 choices and rebuild penalties remain. While RAID 6 adds protection, it does nothing to alleviate the performance penalty imposed during those rebuilds.

Need a more concrete reason not to accept RAID 6 at face value as the panacea your vendor says it is?  Try this.

When writing a second parity stripe, we of course lose about the same amount of disk space as we did when writing the first (assuming the same number of disks are in each RAID group). This means that when implementing RAID 6, we are voluntarily reducing disk storage space to about 60% of purchased capacity (as opposed to 80% with RAID 5). The result: in order to meet anticipated data growth, in a RAID 6 environment we must always buy added hardware.

This is the point at which many readers will sit back in their chairs and say to themselves, “So what?  Disks are cheap!” And so they are — which naturally is one of the reasons storage administrators like them so much. But what if my reader is not in storage administrator? What if the reader is a data center manager, or an MIS director, or a CIO, or a CFO? In other words, what if my reader is as interested in operational expenditures as in the CAPEX?

In this case, the story becomes significantly different. Nobody knows exactly what the relationship between CAPEX and OPEX is in IT, but a rule of thumb seems to be that when it comes to storage hardware the OPEX will be 4-8 times the cost of the equipment itself. As a result, everybody has an eye on the OPEX. And these days we all know that a significant part of operational expenditures derives from the line items associated with data center power and cooling.

Because of the increasing expense of electricity, such sites are on notice that they will have to make do with what they already have when it comes to power consumption. Want to add some new hardware?  Fine, but make sure it is more efficient than whatever it replaces.

When it comes to storage, I’m quite sure that we will see a new metric take hold. In addition to existing metrics for throughput and dollars-per-gigabyte, watts-per-gigabyte is something on which buyers will place increased emphasis. That figure, and not the cost of the disk, will be a repetitive expense that managers will have to live with for the life of whatever hardware they buy.

If you’re thinking of adding RAID 6 to your data protection mix, consider the down-stream costs as well as the product costs.

Does RAID 6 cure some problems? Sure, but it also creates others, and there are alternatives worth considering. One possibility is a multilevel RAID combining RAID 1 (mirroring) and RAID 0 (striped parity), usually called either RAID 10 or RAID 1+0. Another is the “non-traditional” RAID approach offered by vendors who build devices that protect data rather than disks. In such cases, RAID 5 and 6 would have no need for all those recalculations required for the unused parts of the disk during a rebuild.

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The advantages and disadvantages of RAID 5EE

RAID 5EE is very similar to RAID 5E with one key difference — the hot spare’s capacity is integrated into the stripe set. In contrast, under RAID 5E, all of the empty space is housed at the end of the array. As a result of interleaving empty space throughout the array, RAID 5EE enjoys a faster rebuild time than is possible under RAID 5E.

RAID 5EE has all of the same pros as RAID 5E but enjoys a faster rebuild time than either RAID 5 or RAID 5E. On the cons side, RAID 5EE has the same cons as RAID 5E, with the main negative point being that not a lot of controllers support the RAID level yet. I suspect that this will change over time, though.

As is the case with RAID 5E, RAID 5EE requires a minimum of four drives and supports up to eight or 16 drives in an array, depending on the controller. Figure C shows a sample of a RAID 5EE array with the hot spare space interleaved throughout the array.

 

A RAID 5EE array with five drives A RAID 5EE array with five drives

When a drive fails, as shown in Figure D, the empty slots are filled up with data from the failed drive.

empty slots are filled up with data from the failed drive.

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RAID Recovery – Don’t Increase the Level of Difficulty

RAID Recovery More and more enthusiast users encounter the destroyed RAID arrays. Generally, data recovery from such a RAID array is possible, but keep in mind that the effort increases disproportionately. First of all, data has to be copied from a RAID drive onto a server, and the data set has to be put back together. The distribution of data into smaller blocks across one or more drives makes RAID 0 the worst possible type to recover. Increasing performance doesn’t necessarily do your data any good here! If a drive is completely defective, only small files, which ended up on only one of the RAID drives (despite the RAID stripe set), can be recovered (at 64 kB stripe size or smaller). RAID 5 offers parity data, which can be used for recovery as well.

RAID data configuration is almost always proprietary, since all RAID manufacturers set up the internals of their arrays in different ways. However, they do not disclose this information, so recovering from a RAID array failure requires years of experience. Where does one find parity bits of a RAID 5, before or after the payload? Will the arrangement of data and parity stay the same or will it cycle? This knowledge is what you are paying for.

Instead of accessing drives on a controller level, the file system level (most likely NTFS) is used, as logical drives will provide the basis for working on a RAID image. This allows the recovery specialist to put together bits and bytes after a successful recovery using special software. The recovery of known data formats is an important approach in order to reach towards a complete data recovery. Take a JPEG file for example – will you be able to recognize a picture after recovery? Or will you be able to open Word.exe, which is found on almost every office system? The selected file should be as large as possible, so it was distributed across all drives and you can know for sure that its recovery was successful.

Two dead hard drives in a RAID 5 are more likely to be restored than two single platters, since RAID still provides parity data.

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RAID Data Recovery Is Possible!

RAID Data RecoveryWhat if your hard drive decides to enter the Elysian Fields in this very moment? Sure, you could simply get a new hard drive to substitute for the defective one with a quick run to your favorite hardware store. And with last night’s backup you might even reconstruct your installation quickly. But what if you don’t have a backup? The truth to be more like this: many users don’t even have a backup, or it simply is too old and thus useless for recovering any useful files at all. In case of real hard drive damage, only a professional data recovery specialist can help you – say bye-bye to your vacation savings!

Hard drive failure is especially disastrous for smaller companies working with a single server and a single disk, if they do not have a complete and working data backup at hand. The whole situation is even more complicated if the broken hard drive is a member of a RAID array. Neither hard drive failure in RAID 1 nor RAID 5 will result in data loss, since this scenario has been taken care of by the choice of these RAID levels in advance. But the risk of human error increases: self-made data loss occurs if you accidentally substitute the wrong drive in a degraded RAID 5 array (one with a failed hard drive).

But not all hard drives that show failure symptoms are defective. Sometimes, so called “soft errors” can be fixed using data recovery software. But even in this case, you should weigh the risks to see if it makes sense to take care of the problem yourself or get help from professionals. You might not be able to detect a controller failure right away, for example; usually, users assume a problem with the hard drive. Here is our rule of thumb: if you hear clacking sounds in the potentially defective hard drive, or if the computer’s S.M.A.R.T. function indicates an error during the boot process, something is wrong for sure.

What can you do once you know that an important hard drive is definitely broken? Or what happens if you pulled the wrong drive out of the slot while you were desperately trying to save your data? First of all: don’t panic! You need to act systematically and thoughtfully to be successful, as well as to ensure that you spend as little as possible on recovery – costs can hits four digits easily.

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Raid Level 6

Striped set with dual distributed parity. Provides fault tolerance from two drive failures; array continues to operate with up to two failed drives. This makes larger RAID groups more practical, especially for high availability systems. This becomes increasingly important because large capacity drives lengthen the time needed to recover from the failure of a single drive. Single parity RAID levels are vulnerable to data loss until the failed drive is rebuilt: the larger the drive, the longer the rebuild will take. Dual parity gives time to rebuild the array without the data being at risk if a (single) additional drive fails before the rebuild is complete.

Raid Level 6
Advantages

  • RAID 6 is essentially an extension of RAID level 5 which allows for additional fault tolerance by using a second independent distributed parity scheme (dual parity).
  • Data is striped on a block level across a set of drives, just like in RAID 5, and a second set of parity is calculated and written across all the drives; RAID 6 provides for an extremely high data fault tolerance and can sustain multiple simultaneous drive failures
  • RAID 6 protects against multiple bad block failures while non-degraded
  • RAID 6 protects against a single bad block failure while operating in a degraded mode
  • Perfect solution for mission critical applications

Disadvantages

  • More complex controller design
  • Controller overhead to compute parity addresses is extremely high
  • Write performance can be brought on par with RAID Level 5 by using a custom ASIC for computing Reed-Solomon parity
  • Requires N+2 drives to implement because of dual parity scheme

Recommended Applications

  • File and Application servers
  • Database servers
  • Web and E-mail servers
  • Intranet servers
  • Excellent fault-tolerance with the lowest overhead

RAID 6 VS RAID 5

RAID 6
In complex arrays (12-24 drives), RAID 6 applications would be a preferred choice due to the fact that Serial ATA drives used in the arrays have a lower duty cycle and may be more likely to fail in 24/7 or business-critical applications.

Raid 5
In small arrays (4-12 drives), RAID 5 applications can quickly repair a failed drive and restore lost data-without taking down the array. It’s perhaps the most cost-effective, fault-tolerant data protection solution currently available for small storage devices.

Pro
Raid 6
Designed for tolerating two simultaneous HDD failures by storing two sets of distributed parities.

Raid 5

  • Simplified hardware implementation
  • A matured industry standard

Con
Raid 6

  • For RAID 6, one needs a more complex system with a method for encoding, as well as XOR calculations. For that, one really needs hardware acceleration, otherwise the performance suffers.
  • Uses 2 drives for parity

Raid 5

  • The risk of simultaneous drive failures grows in proportion to the drive array and can increase if customers purchase all of the disks in an enclosure at one time.
  • If the system finds a faulty sector on another drive during this degraded state (one drive down, spare drive being rebuilt), the RAID 5 system would be unable to restore the data onto the spare drive, resulting in data loss.

Recommended Configuration
Raid 6
Disk array consists of 12 disks or more

Raid 5
Disk array consists of 10 disks or less

Recommended Solutions

Raid 6

  • Desktop: EnhanceRAID T8
  • Rackmount: EnhanceRAID R14; UltraStor RS16

Raid 5

  • Desktop: EnhanceRAID T4HCR, T5,T8
  • Rackmount: EnhanceRAID R4,R6,R8; UltraStor RS8 or RS2080

Raid 6 Rebuild Software

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Software RAID VS Hardware RAID

RAID stands for Redundant Array of Inexpensive Disks which is a technology that employs the simultaneous use of two or more hard disk drives to achieve greater levels of performance, reliability, and/or larger data volume sizes.

There are different levels of RAID. The most popular RAID formats are RAID-1 & RAID-5. However today we will not focus on the various RAID format. Let’s go straight to the differences between software RAID and hardware RAID.

1. Hardware RAID:

  • A conventional Hardware RAID consists of a RAID controller that is installed into the PC or server, and the array drives are connected to it.
  • In high end external intelligent RAID controllers, the RAID controller is removed completely from the system to a separate box. Within the box the RAID controller manages the drives in the array, typically using SCSI, and then presents the logical drives of the array over a standard interface (again, typically a variant of SCSI) to the server using the array.

2. Software RAID:

In software RAID the software does the work of RAID controller in place of the hardware. Instead of using dedicated hardware controllers or intelligent boxes, we use particular software that manages and implements RAID array with a system software routine.

3. Comparing Hardware RAID & Software RAID

Portability

OS Portability

Software RAID is not usable across operating systems. So you cannot, for example, use two RAID disks configured in Linux with Windows XP and vice versa. This is big issue for dual booting systems where you will either have to provide a non-RAID disk for data sharing between the two operating system / use hardware RAID instead.

As you know, dual booting is mostly obsolete these days as you can run multiple operating systems on the same machine using virtualization software like VMware & xen.

Hardware Portability

  • Software RAID
    In Linux you can mirror two disks using RAID-1, including the boot partition. If for any reason the hardware goes bad, you can simply take the hard disk to a different machine and it will just run fine on the new hardware. Also with a RAID-1 array, each of the hard disk will have full copy of the operating system and data, effectively providing you with two backups, each of which can be run from a different hardware.Unfortunately in Windows it is not so easy to switch a operating system from one hardware to another, but that is the story of proprietary licenses and we will keep it for another day.
  • Hardware RAID
    Hardware RAID is not so portable. You cannot just swap the hardware to a different machine and hope it will work. You have to find a Motherboard which is compatible with your RAID controller card; otherwise you can kiss your data goodbye. Also there is a bigger issue of problem with the RAID controller itself. If it fails and you cannot get the same controller from the market (and it has probably become obsolete by then), then again you can kiss your data goodbye.

Easy & Speedy Recovery

It may seem trivial but for a busy and loaded server, an easy and speedy recovery, that too inside the operating system without having to reboot is what one can dream of. Imagine if during the peak hours, your RAID system crashes and you are forced to reboot the machine to make changes to it to restore your data! Software RAID’s like in Linux, not only continues working even when the hardware has failed, but also starts restoring the RAID array, should any spare disk be available. All of these happen in the background and without affecting your users. This is where software RAID shines brilliantly.

System Performance

Software RAID uses the CPU to do the work of the RAID controller. This is why high-end hardware RAID controller outperforms software RAID, especially for RAID-5, because it has a high powered dedicated processor. However for low end hardware RAID, the difference may be neglible to non-existent. In fact it is possible for the software RAID perform better than low end hardware RAID controller simply because today’s desktops and workstations are powered by very powerful processors and the task is trivial to them.

Support for RAID Standards

High-end Hardware RAID may be slightly more versatile than Software RAID in support for various RAID levels. Software RAID is normally support levels 0, 1, 5 and 10 (which is a combination of RAID 0 and RAID 1) whereas many Hardware RAID controllers can also support esoteric RAID levels such as RAID 3 or RAID 1+0. But frankly who uses them?

Cost

This is where software RAID again scores over hardware RAID. Software RAID is free. Hardware RAID is moderate to high priced and can put a strain on your budget if deployed widely.

But over the years the cost of hardware RAID has come down exponentially, so it may not be too far when more affordable RAID-5 cards will be built-in on newer motherboards.

Future Proof

Gone are the days when we could associate software RAIDs with bugs and OS problems. Nowadays software RAIDs are almost flawless. We are using software RAID in Linux operating system for several years and haven’t experienced any problem whatsoever. On the contrary, hardware RAID has a single point of failure and that is its hardware controller. If it crashes then your only option is to find another equivalent RAID controller from the market; by this time the model may become obsolete and you may not even find anything compatible. You are as such faced with the haunting prospect of losing all your data, should the RAID controller fail. Software RAID will never become obsolete and will continue to get updated with updated versions of your operating system.

4. In conclusion: Software or Hardware RAID?

In my opinion, software RAID is the way to go for most users, unless you want to extract the very last ounce of performance from your RAID array and budget is not a constraint.

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