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In the most general sense what is an array and what is a group (also what's a virtual drive)? From here:

Redundant array of independent disks (RAID) is a storage technology used to improve the processing capability of storage systems. This technology is designed to provide reliability in disk array systems and to take advantage of the performance gains offered by an array of multiple disks over single-disk storage.

This makes it sound like an array can exist without RAID. When configuring RAID in webbios (in LSI MegaRAID) it uses the word group, what does that mean? In this context it seems to mean any disks that aren't part of an array but will be in the future.

Since a system can have more than one independent raid configurations, what would that be called? For example if a system had two harddrives in RAID 0 and another 2 harddrives in RAID one, would the system be said to have two RAID arrays?

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2 Answers 2

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This makes it sound like an array can exist without RAID.

Yes, you are looking for Non-RAID Drive Architectures such as JBOD. But an "array" is basically just one or more disks that has something going on with it (at some level; not necessarily at the controller level; it could be in software) that isn't just using it by itself. You could call this an "array" if you want, but it's not a RAID array; again, just terminology/semantics.

...it uses the word group...

Just alternative terminology. You should've specified that "webbios" is in the LSI MegaRAID firmware; I had to look around to find out what it is. :-/

...would the system be said to have two RAID arrays?

Yes.

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So if you just happen to have two disks in your computer would you call that an array? –  Celeritas May 8 at 18:21
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@Celeritas It's just semantics! In what sense would it be an array? Well, it depends on how you define "array"! Do you choose to define "array" to mean that the disks have to be configured in a RAID level? Do you define "array" to mean that the disks are spanned together using Windows' Dynamic Disks or LVM? Or are disks in an "array" if you have completely separate C: and D: drives that are not related in any way? Most people wouldn't consider that an array, but you wouldn't be crazy to define it that way; you'd just have an arbitrarily different definition than most people. *shrug*. –  ÃŁŁǫǛȉЖΦΤїҪ May 8 at 18:23
    
Right so what I get out of this is there's no set-in-stone definition to array and could mean different things depending on context/speaker (even within the context of disk storage). –  Celeritas May 8 at 18:24
    
Yes, and indeed many different hardware vendors (RAID controller vendors, whole-server vendors like HP and Dell, etc.) use different terminology to refer to the same thing. When you're dealing with this kind of thing, you really have to learn the individual vendor/company's specific terminology, by reading their manuals or blogs or technical documents, to figure out precisely what they mean. The term "RAID" itself is reasonably well-defined, but there is still some disagreement about what RAID levels are possible; what RAID levels are good; and what each RAID "number" means. –  ÃŁŁǫǛȉЖΦΤїҪ May 8 at 18:25

An array is an ordered collection of objects, but in this case, a raid array is a single set of disks whose operations are coordinated. RAID is the primary hardware approach to creating storage arrays, so yes, a set of disks whose operations are not coordinated are not in an array, especially not a raid array.

Yes, in your example, your system would have two raid arrays.

Storage Arrays may have dozens or hundereds of drives, so you can tell the system to take 10 of them and establish a raid array from them. I believe that this is what is being refereed to as a group (the subset of disks that will make up the array). That way you can say "this server gets 5 disks" and "That other server gets 7", and dice up the storage hardware in that manner.

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