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If no, how do people run synology in RAID 1 and it only shows 1 bigger drive. I'm a bit new to this.

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    What have you tried and what have you found that doesn't match your expectations? Please edit and expand upon your question.
    – Greenonline
    Commented Jul 27, 2022 at 11:16
  • The title is not the question. Please edit your question and title to make it more clear what you are asking
    – music2myear
    Commented Jul 28, 2022 at 4:29

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There are many different possibilities here.

First, you can have hardware or software RAID. Hardware RAID is the "true" one which is OS independent and the OS does not even know how the RAID is internally organized. Hardware RAID controller combines disks into RAID arrays and presents each array as a single disk to the OS. From the OS point of view, it is a "physical" disk (although it may actually consist of two or more actual physical disks).

Software RAID works on the OS level. Low-level OS drivers "see" each disk independently. These drivers combine disks into RAID arrays and present them to the higher OS layers as logical disks.

Regardless if hardware or software, RAID 1, strictly speaking, consists only of a pair of mirrored disks (must be the same size) that is treated like a single disk. So, if you have two 3TB drives in RAID 1, your OS would use them as a single 3TB disk. Any of the disks in a RAID 1 pair is an exact copy (mirror) of the other.

Something totally different is RAID 0, or so called striping. Here, two or more disks (do not need to be the same size) are "joined" together to form a single large disk whose size is the sum of sizes of all component disks. So for example, if you had four 3TB drives in RAID 0, this would be equivalent to having a single 12TB disk.

These two have completely different purpose. RAID 1 is for data protection against a disk failure (if one disk fails, the data is still on the other disk, so you can replace the faulty disk with a new one - with good quality RAID controllers this can be done even in a running system, without shutting it down - and the data will be gradually copied to the new disk). RAID 0 is purely for size and speed (access to 4x3TB disks in RAID 0 is faster than to single 12TB disk, assuming that such a disk exists), there's no protection against failure.

So you can combine one with the other resulting in something called RAID 1+0 (sometimes written as RAID 10). Here you have two levels. First level are two or more RAID 1 pairs. Each of them forms a single "component" disk for the upper level, which is RAID 0. So you take mirrored disk pairs and join them to form one larger disk. Here is an example diagram of how RAID 1+0 storage is organized:

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It should be also noted that you can have these two layers implemented independently, for example you can create a few hardware RAID 1 arrays, and have them joined into a single disk with software like Linux's LVM (Logical Volume Manager), that allows to create one logical disk spanning multiple "physical" disks (here "physical" disks being actually RAID 1 pairs).

Sometimes you can also encounter RAID 0+1 configurations. It's implemented in reverse order as RAID 1+0: first you have two RAID 0 disk sets (they must be equal in size), and then they are mirrored into a RAID 1 pair. But this is rarely used, compared to RAID 1+0.

Finally, there is RAID 5. It uses three or more drives (of the same size) to spread data equally across all drives. If you have for example 4 drives in RAID 5, for every three blocks of data written to the RAID device, each block is written to one of the three drives, and a checksum block (which allows for data recovery if one of the disks fail) is written to the fourth drive (a different one for each three blocks). So with 4x3TB drives in RAID 5, you can effectively use 9TB, while in RAID 1+0 you can use only 6TB). However, disks in RAID 5 are more heavily used than in other RAID configurations, so the time until they fail may be shorter.

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  • thanks for your detailed answer. take my upvote.
    – PyCoder01
    Commented Jul 27, 2022 at 17:58
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For the operating system, the RAID drive looks like one disk.

RAID 1 on the 4 drives would be one 3TB drive mirrored 3 times. You might want to have two RAID 1 mirrors on each pair of disks, which would give you two disks of 3TB each.

For one disk of 6TB you need RAID 1-0.

For one disk of 9TB use RAID5.

References:

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  • So If I had 4 3tb drives in my RAID Box on raid 1 it would show up as a 6tb drive in my file manager?
    – PyCoder01
    Commented Jul 27, 2022 at 13:08
  • so the full 6tb would be usable.
    – PyCoder01
    Commented Jul 27, 2022 at 13:14
  • I answered above.
    – harrymc
    Commented Jul 27, 2022 at 15:10
  • If my answer was helpful, please consider marking it as accepted (click the ✔ sign).
    – harrymc
    Commented Jul 27, 2022 at 15:12
  • you literally copied the other post and edited yours.
    – PyCoder01
    Commented Jul 27, 2022 at 18:00

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