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Understand how much space is used for data redundancy
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11/29/2012 – Having a NAS and a bunch of hard drives to store your data isn't all that is needed to keep them safe. To manage the way you want your data to be stored across all of your hard drives, you need to specify which RAID mode will control your volume. Although RAID can increase data access speed and security, it comes at a cost. Either you need to sacrifice speed for redundancy or space for security. In here, we'll go into details on the available RAID modes and how much space they may use to make your data secure.


The acronym stands for “Just a Bunch Of Disks” and its name define clearly its purpose. JBOD takes to totality of the drives in your NAS, creates a volume that will act as one, and start storing the data beginning with disk one and , when full, moving to the next one. Technically speaking, it is not a RAID as no redundancy is achieved but it also means that no space is sacrificed and that the totality of the disk space can be used. So for our example, the math will be simple:

# of HDD (n) Total capacity Space used for redundancy Total space available
6 x 1TB 6TB 0 6TB (100%)


This mode is similar to JBOD because no space is sacrificed and that there is no data redundancy. What makes this mode different is that the data is spread within the hard drives, meaning that all drives fill up pretty much evenly at the same time. One thing to note though is that if when creating a RAID 0 with different size drives, the maximum capacity used on each drive will be equal to the smallest one only. So if you have a RAID 0 with 2 drives, one of 1TB and the other one of 2TB, your total capacity will be restricted to 2TB instead of 3. It is thus recommended to use same size drives within a RAID volume.

# of HDD (n) Total capacity Space used for redundancy Total space available
6 x 1TB 6TB 0 6TB (100%)


RAID 1 is the first mode to introduce some kind of redundancy within a volume; therefore using some of your physical space to make sure your data is safe. RAID 1 is simple and requires a minimum of 2 hard drives to be created, while the first hard drive is used to store your data, the second one is used to create a copy of that data, this process is also called mirroring. It is the most expensive method as half of your physical space is sacrificed for redundancy, but as an advantage of that sacrifice, you may have one hard drive failing without losing any of your data.

# of HDD (n) Total capacity Space used for redundancy Total space available
2 x 1TB 2TB 1TB 1TB


The very famous RAID 5 sacrifices less storage. The concept is simple, out of all the disks, the space of 1 is used for redundancy, but like RAID 0, it is spread around all the disks. The best way to describe this mode is by giving an example. Let's say we have 4 HDD built in RAID 5 mode, each hard drives has a capacity of 1TB. Each drives gets divided into blocks of storage, we'll say 4 for our example. As your data gets recorded on the HDD, they are spread across the first drives (A1, A2, A3), then for the A4 block, a recovery is created with the parity of the stored data in the other block. As you don't want your redundancy to be all in the same place, you'll need the recovery block to be on a different disk for the other lines of storage as shown in the image here. Although the whole space of one disk is used for redundancy, one HDD can fail and be recovered without data loss or disrupted access to the data.

# of HDD (n) Total capacity Space used for redundancy Total space available
6 x 1TB 6TB 1 TB 5TB (n-1)


RAID 6 is a more secure mode than RAID 5 as the space of two HDDs, instead of only one, is used for redundancy. The major advantage over RAID 5 is that two HDDs can crash at once and still all the data will be available and none of it will be lost.

# of HDD (n) Total capacity Space used for redundancy Total space available
6 x 1TB 6TB 2 TB 4TB (n-2)


The Thecus® NAS can support various mode of RAID and even multiple RAID options on some models for better and customized data redundancy. To find out which NAS can support which mode, please visit Thecus® official website.

About Thecus®
Established in 2004, Thecus Technology Corp provides market leading network attached storage and network video recorder solutions, committed to revolutionize how everyone from home user to enterprise level business centrally stores, manages and accesses their digital data both onsite and cloud-based. Thecus strives to deliver continuous innovation through cutting edge technology and design to provide data storage with the most customer-friendly platform, rapid performance and robust security. In May 2016, Thecus was formally acquired by Ennoconn Corporation and thus became part of the Foxconn IPC Technology group. Partnered together this diverse group of companies work in tandem to provide a total IoT (Internet of Things) solution. Now with an unparalleled portfolio to work with, Thecus is collaborating to bring unprecedented change to the network storage industry.