[SOLVED] Higher capacity RAID?

nhpr

My Google skills have failed me because I'm too ignorant to even find the proper search terms!

Let's say I'd like a nice NAS server, database storage, or something along those lines and would like it backed by RAID 10. Since RAID 10 capacity is 2 * smallest HD, what happens when you need more space than would be afforded by two disks (like say 70TB)? Do you just slap several RAID arrays together into a single logical volume? Build a SAN instead? I'm assuming the answer depends on a number of factors, so let's limit it to the most common answer to this problem.

instant000

nhpr wrote: »

My Google skills have failed me because I'm too ignorant to even find the proper search terms!

Let's say I'd like a nice NAS server or something along those lines and would like it backed by RAID 10. Since RAID 10 capacity is 2 * smallest HD, what happens when you need more space than would be afforded by two disks? Do you just slap several RAID arrays together into a single logical volume? Build a SAN instead? I'm assuming the answer depends on a number of factors, so let's limit it to the most common answer to this problem.

USDA ? I'm having to google that one, LOL. I'm thinking about food when seeing that one. (EDIT: realize it must be a joke, haha.)

But, immediately, to answer your question:

To answer your question, it is about expanding your array? To expand your array, you just add more drives, up to the limit given by your controller. With some controllers, it is a low number of drives: ten or less. With other controllers, you can add dozens and dozens of drives to a single array.

Also, with any sort of RAID, you're limited by the smallest disks that you place in the array.

That is, if you have an array with a bunch of 160 GB disks, and then you add some 320 GB disks to the same array, it is as if you just added more 160 GB disks, and you just wasted space on those drives.

With regards to just slapping several arrays together, and making logical volumes out of them ... I've only done this when the arrays were attached to the same controller. That is, I've not spanned several controllers, then created LUNs. (I've spanned several drive bays, but they were all under the same enterprise array set. e.g.: set of 96 drives across 8 shelves, or some such, but it's under the same main controller set. I've not spanned volumes across array sets, so I'd not know the technicals behind that one.)

Does this explain things?

Anyway, I think they covered RAID in Server+, and if that fails you, I'm sure there is a wikipedia entry on it, to get you started.

Standard RAID levels - Wikipedia, the free encyclopedia

You would be best-advised to ask questions about this in the Server+ forum, as this is that type of question.

I hope I didn't just confuse you more ...

nhpr

instant000 wrote: »

USDA ? I'm having to google that one, LOL. I'm thinking about food when seeing that one. (EDIT: realize it must be a joke, haha.)

It's no joke. I'm both tasty AND safe to eat.

But, immediately, to answer your question:

To answer your question, it is about expanding your array? To expand your array, you just add more drives, up to the limit given by your controller. With some controllers, it is a low number of drives: ten or less. With other controllers, you can add dozens and dozens of drives to a single array

I had a bit of a mental lapse. I've only seen RAID controllers with four available "slots," so it had never really occurred to me that you can stick more drives into them given an adequate controller. This reminds me of the time when I was two and, after watching Sesame Street only count to 20 numerous times, I decided that there were no numbers beyond that.

MentholMoose

nhpr wrote: »

This reminds me of the time when I was two and, after watching Sesame Street only count to 20 numerous times, I decided that there were no numbers beyond that.

Reminds me of this:
YouTube - hilarious asian counting in english

jibbajabba

I only ever played with Adaptec cards really, but on those you can easily extend the array. Let's say you got a 4-Disk Raid 10 with 4x160GB. You can just pull one disk, add a larger disk, let it rebuild, pull another 160 and ad a 320, let it rebuild and so on until you swapped all 4. Once all 4 are swapped you can grow the array and then extend the filesystem inside the OS ... That doesn't require any downtime and that is what we are doing almost daily with customer needing to upgrade their NAS. Although if it's a NAS, you could also simply convert the array into a Raid5, gaining more space immediately. So instead of a 4x160 Raid10, which gives you 320GB useable, in a 4x160 Raid 5 you got 480GB useable. Again, Adaptec supports that but i don't know about others, I think Areca and 3Ware do that too.