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What is Disk Duplexing?
Disk duplexing refers to a specific process followed for writing information or data to more than one hard drive on separate disk controllers. The process allows for writing data to two different drives on the same system.
More specifically, this is a method to record redundant data specially intended for fault tolerant operations. Technically, in this process, every disk drive is connected to an individual controller.
- Disk duplexing is the particular process of writing data on different hard drives with separate drive controllers. This makes it quite a reliable option.
- This process is often confused with the disk mirroring process that also allows writing to redundant disk drives but by using only a single, common disk controller.
- Duplexing on hard disks allows for fault tolerant procedures and especially helps in the internetworking of computers.
- Disk duplexing helps a lot in RAID settings since the group of hard disks improves the performance by operating together and providing error recovery and fault tolerance.
- It is a relatively less expensive way of protecting data in comparison to data mirroring because it needs less storage space for the purpose.
Understanding Disk Duplexing
When data or information is written on two different hard drives by using two different disc controllers for each, it is called disk duplexing.
Since disk duplexing involves the copying of data in such a way, it may be conceptualized as data mirroring.
Though the disk duplexing process is quite similar to disk mirroring, in effect, it uses separate disk controllers or host adapters as opposed to the one used in the data mirroring process.
This means that data mirroring is a type of data duplication by using a single channel, but disk duplexing typically refers to data copying on hard drives on separate channels.
At this point, it is important to note that mirroring a hard drive to another physical disk in a system is allowed only when both of these drives are of the similar logical size.
Typically, the data storage units such as the tape backups and disk subsystems perform as the fundamental components for Local Area Network (LAN) and Wide Area Network (WAN) that allow for internetworking.
Ideally, it has become the fastest growing zone within the computer industry due to the crucial role that these components play.
These components underline the significance of ensuring the integrity of data especially in the mission critical environments.
Disk duplexing, along with disk mirroring, is the most popular means for addressing this specific necessity in networking.
The importance of disk duplexing can be best understood when you know the nature of the hard drives.
Typically, the hard drives are mechanical entities since they come with moving parts inside, such as the spinning disc, which is why they are also referred to as hard disks.
Just like any other mechanical device, the physically moving parts inside the hard drives are more vulnerable to failure due to wear and tear.
Disk duplexing on the hard drives helps in maintaining copies of every bit of data on a physically separate drive within the computer system.
In the event of disk failure on the primary drive, the secondary drive functions as the backup unit.
This, therefore, prevents delays in the operation or it stops completely. And, as said earlier, disk duplexing maintains data integrity within the disk subsystem.
Fault Tolerance Concept
Typically, the disk duplexing phenomenon is based on the fault tolerance concept derived from Redundant Array of Inexpensive Disks or RAID.
Fault tolerance guarantees improvement in performance on the basis of disk duplexing on a group of hard disks.
These disks operate together to allow for error recovery as well through different techniques such as:
- Data mirroring
- Data striping
The two physical drives with individual controllers are plugged into the motherboards that do not have RAID circuits.
Most motherboards today, however, have it built into them but that does not mean all of them come with all of the RAID configurations.
In larger Storage Area Networks (SAN), usually with a couple of terabytes of storage, usually have floor-standing RAID units.
Disk duplexing allows additional data protection when a hard disk fails or when the hard drive channel between the server and the particular disk fails.
As already mentioned, it is provided by copying data onto two separate hard drives at the same time but each of them on a different disk channel.
This hard disk channel comes with the following:
- A disk controller
- An interface cable
Since each drive is on a separate channel, there is no interruption in the work routines or data loss even if one component on a particular channel fails.
This provides the users with a chance to reinstate the duplexing protection after the failure as soon as possible without letting the workflow be interrupted.
Disk duplexing has a few specific features that are also good to know at this juncture.
Complete data protection is not guaranteed:
Disk duplexing by itself does not assure complete data protection. This is because the chances of both the drives failing at the same time, or even the computer system as a whole, still exists.
This means that your data can still be potentially lost forever. Therefore, create a proper backup of your data on a regular basis.
Faster data transfer:
As said earlier, disk duplexing involves copying data on a different drive through different channels at the same time.
This allows a much faster data transfer than disk mirroring which involves only one channel while writing data to two different physical disks.
Disk duplexing allows split seeks as well, where read requests are sent to the disk that responds first.
Even if there are several read requests, these are split between the two duplexed disks. This allows for simultaneous data processing.
Disk Duplexing vs Disk Mirroring
- Disk duplexing involves creating two separate copies of the data on two separate different drives. On the other hand, disk mirroring involves creating the same copy of hard drives, programs or files on another drive which is then used as a backup when the original is damaged or lost.
- Disk duplexing is a process typically followed for larger amounts of data that do not need backing up often. On the other hand, the disk mirroring process is normally used for small amounts of data that need to be backed up often.
- Data duplexing is the process of storing the same data on two separate disks on two separate channels. On the other hand, data mirroring is the process that involves only one single channel while storing the same data on separate disks.
- Data duplexing is relatively more reliable than data mirroring because it uses two different drivers or channels, which are highly unlikely to fail at the same time.
- As far as the cost factor is concerned, data duplexing is a less expensive way to protect data in comparison to data mirroring because the latter needs almost double the amount of disk storage as compared to the former.
- The throughput and performance of data duplexing are both relatively much more improved in comparison to the performance level and throughput of data mirroring.
As you can see from this article, duplexing is quite a useful way to protect data.
It is very easy to use and is also quite a cost-effective way to add to the integrity and reliability of data, which is mainly because it is done by using two diverse channels.
It is best for large sets of data that do not need regular backing up.