Question Two newbie questions about Zyxel NAS542

supacoopa

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Hello everyone.

I'm about to purchase a Zyxel NAS542 and have the following questions, for those in the know.

1. Is it possible to configure the device to allow indepedent access to each of the four disks?
I believe this is called a "Basic" or "Standard" array and is different to JBOD in that storage space is not unified across disks, but split in relative volumes.
So does NAS542 allow this setup, so that each disk would be a different volume and can therefore be taken out of the NAS, without affecting the rest of the array?

2. Is it possible to expand a "Basic" or JBOD array, by adding new hard disk(s) without the need to format existing disks?
In other words I want to start with one or two disks, fill them with content and then at a later date add one or two more new disks without losing existing data on the previous disks.

I have searched for answers on the downloadable manual but couldn't find any, so any help is greatly appreciated!
 
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I cannot speak for your particular model of NAS, but generally JBOD - (Just a Bunch Of Discs) is what you seek. Each disc functions independently of all the others, there's no "relationship" between them, the space is not "pooled" or "unified" across the discs. You need RAID arrays or "drive pools" (or something similar) to do that kind of thing.

How you "access" each disc across a network is a function of how you create the network shares not the disc structure/arrays. A network share essentially "points" to a particular place in the disc/file structure. They could be anywhere, including the "root" of the file structure on a particular disc.

So for example, there no reason why you could not create shares called "drama" "comedy" "movies" all pointing to different parts of the file structure on disc "A," but equally you could create "drama" pointing to root of disc A, "comedy" pointing to the root of disc B, "movies" to the root of disc C, etc. (With the advantage that if ever you move things around within/between discs, you can thence change where the shares point and your client devices are none the wiser.)
 
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I was under the impression that JBOD is only supposed to unify all disks, resulting in a single logical volume, spanned across all physical disks. So is it possible to have, say, 4 "independent" disks in a NAS, configured as JBOD?

I would have no problem with the "unified space" configuration, have I not read that if one disk fails, the whole JBOD array becomes useless. Isn't it so?

But anyway, my main concern is whether I will be able to gradually build any kind of non-RAID array, using two disks to begin (this is pretty straightforward) and then adding another one or two, without losing content present on the "older" disks.
 
With the caveat that your NAS may do something "special," but in general terms (and all the motherboards and RAID controllers I've configured..)

I was under the impression that JBOD is only supposed to unify all disks, resulting in a single logical volume, spanned across all physical disks. So is it possible to have, say, 4 "independent" disks in a NAS, configured as JBOD?

No: JBOD is just that - a bunch of discs in a chassis. "JBOD" is often a term used in the configuration of RAID controllers to describe the situation where the discs are "not in some for of RAID configuration." So (for example) the controller would offer a choice of RAID1 (mirrored) RAID0 (striped) or JBOD (nothing.)

The sort of descriptions you are ascribing to JBOD would be something like RAID0 or a "drive pool."

JBOD usually means all the discs function independently of each other and you can add/remove/change them at will as altering one has no effect on the others. (Which is most decidedly not the case with any RAID configuration.)

I would have no problem with the "unified space" configuration, have I not read that if one disk fails, the whole JBOD array becomes useless. Isn't it so?

Again, no - this is a function of RAID arrays. Removing a disc from a RAID0 (striped) array would render the entire array unreadable. (RAID1 & RAID5 does something different.) In JBOD's the other discs should be unaffected.

But anyway, my main concern is whether I will be able to gradually build any kind of non-RAID array, using two disks to begin (this is pretty straightforward) and then adding another one or two, without losing content present on the "older" disks.

Should be fine with JBOD.

If you want to know about RAID, Wiki's articles aren't bad.
 
Thank you for your detailed answer.

I will have a long read of Wiki's articles, for sure.
 
This might help ftp://ftp.zyxel.com/NAS542/application_note/NAS542_1.0.0.pdf
 

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