[amagab]

I'd like to know how to expand a RAID array if needed. Let's say I have an array with 16 bays. I buy hard drives to fill 4 of the bays and create a RAID. Then, in a few years, I'd like to expand it and add 4 more hard drives. What is the process of doing so? Will there be data downtime?

Thanks!

[besson3c]

I believe this depends on your RAID controller and filesystem.

If you are really interested i doing that, I would suggest looking very hard at running ZFS on Solaris, OpenSolaris, or FreeBSD. Using ZFS you can easily combine drives into groups of three and build RAID-Z sets that you can then stripe with the other sets, or just straight RAID-10 style mirrored sets. In ZFS you can do all of this dynamically without having to reformat or anything, it's very easy and quite elegant - completely software driven.

In a non-ZFS based filesystem, at best, AFAIK, you'd be able to create a new RAID set out of your remaining disks, but this disk would be a completely different set than your original set.

[amagab]

Are you saying that I would have to clone, then add drives, and then load the clone?

[besson3c]

No, I'm saying that AFAIK in traditional RAID setups you can't add drives to an existing RAID configuration, you can only build additional RAID configs which would be presented as a second, separate disk.

[amagab]

I meant to include "rebuild array" in my previous post. So that would work?

[reader50]

Some RAID controllers support online capacity expansion, where you add physical drives. The array will adjust the striping as needed until the virtual drive is bigger. You'd still need to adjust the partition to include the extra space.

In the midrange prices, some HighPoint RocketRAID cards support this. I'd expect it to be a more common feature on the high end.

[besson3c]

AFAIK (and I say AFAIK because it has been years since I've used a traditional RAID setup, I've been using ZFS for a while which is a different animal), you can't rebuild a RAID array without formatting the entire thing.

If you decide to look into what reader50 is saying, I bet you could grow the partition to fill the space allocated using a tool like gparted if your RAID controller was supported by the gparted boot CD. Unless you have a second machine, the machine connected to the RAID array will also have to be down while this operation was performed. All of this is probably not something I would try with live data unless you have a backup.

It would be nice if OS X included something like Linux LVM to be able to expand partitions.

[reader50]

I've heard Apple includes a utility called Disk Utility that can resize partitions. iPartition does too, with far greater control.

note: DU won't do this for DU software RAIDs. So it only applies to RAIDs supplied by controllers.

[besson3c]

Will DU extend partitions for regular direct attach disks?

[reader50]

Apparently so. I haven't had the guts to try it yet. And I already own iPartition, so I've sent all the resizes through it.