Newbie: Why two drives?

I have purchased a model EX2, and it’s working fine.
I’d like to know why it appears to have two drives?
Is the second one only adding space?
Can they be separately addressed?
What model is appropriate for real-time mirroring/backup?

Thank you

Thank you.
When I look at the Admin-interface:Storage:RAID,
under “RAID” I see:
Volume_1 RAID-1 1.96 TB Good.
Based on this can you tell what setting I have?
Is Volume_1 the same as Drive-1 seen under the Disk-Status?
Where is the setting to select RAID-0, 1, or JBOD?

newbie questions are good.

SO - - -there is a thought - - - -that “mirrored” hard drives are good.
The nominally most delicate and shortest lived component in a system, The Hard Disk,
is MIRRORED. . . .so if one drive fails, you simply pop out the bad disk. . .pop in a new disk. . .and the second drive mirrors back to the first drive.

This is Raid 1. Much to be said for it.

Primary downsides;

  • It takes 2 equal sized disks to store one disk of data. (duh). There are more “space efficient” options if you have a 4 or more bay NAS system.

  • Having a mirrored drive invokes a false sense of security - - as you are still vulnerable to viruses; Enclosure failures or other forms of “common mode”; such as FIRE.

In reality; a NAS with Raid1 is really PART of an overall strategy that should include an OFFSITE backup.

Raid 0 - - - writes data across both drives. . .theoretically doubles read/write speeds. From a reliability perspective. . . lose one drive ALL the data on both drives is gone.

JBOD. . . Just a Bunch of Disks… . . .Basically; both HDD’s operate independently. No redundancy. However, both disks will be visiable on your network as independent shares. (not a bad option)

SO - - - if your primary objective is backup. . . really JBOD or Raid 1 is the way to go.
Personally, I use a 2bay Raid1 NAS as a backup - - -plus an additional drive with another copy of the data that is normally somewhere not in my house

Very kind of you, thanks!
I may be missing something but since failures are often in the physical hardware, mixing a back-up drives into a volume defeats the purpose of RAID. But we can leave this question.
I do appreciate your emphasizing the need for real back ups.
I’ve learned that you can’t make enough back-ups near and far (I had an office in the what used to be called the world trade center) ; currently we’re making seven separate back ups: five local and two remote.

If you have the patience:

  1. where is the setting for the other two options?
  2. I assume in the event of a failure the Notifications will let me know explicitly? Is the fail-over automatic?
  3. Is there a reference I can keep that describes the procedure for replacing the failed drive?