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voodoosand · Sep 8, 2002, 12:09 AM

So... I'm trying to set up RAID but I am very new to the process. From what I have read, I can take my existing 60 and 40 GB drives (neither of which is my startup) and using a striped array(?) create a volume that appears to be about 80 GB. The purpose is to backup about 60-some GB of mp3's which are crucial to my survival on this planet. Has anyone had success or experience with this under Jaguar? Of course, read/write speed is not nearly as important as data "safeness". I am somewhat UNIX-aware, so if there is a CLine version that gives me that wasted 20 GB back, that would be fandoobleetastic.
I can't remember if they are, but do the drives need to be the same speed (RPM?) I think one might be a 5400...eewwwww.
Thanks in advance for any info.

snerdini · 12:38 AM

If you want data redundancy with only 2 drives, don't stripe. You want to mirror (RAID 1). Which will be only as big as your smallest drive, 40GB. But that will give you an exact copy of all your data on the other drive (thus, mirror) so if anything ugly does happen, all your data is still safe.

At least in theory. It would be very unlikely that both drives would fail simultaneously, but it could happen...

[edit]
If you have the mp3's on your startup drive, and want to back them up onto the 60 and 40GB drives, that's another story. The drive that you are mirroring from needs to be in the array, and if that's your startup disk, then you need a bootable RAID array. I'm not sure how Mac OS X handles this. It may require a hardware RAID card, I really don't know. But it definitely makes things more complicated.

I would recommend having your mp3's on a drive other that your boot drive, that way you aren't involving the OS in the RAID array. Since all you want is to backup the mp3's, it would help simplify your setup considerably.

Camelot · Sep 8, 2002, 03:42 AM

You're right in that Apple's Disk Utility will create an 80GB volume if you stripe your 40GB and 60GB drive.

There is no way to recover the lost 20GB on the 60GB drive.

As snerdini said, if you wand redundancy, mirroring is the way to go, but then you only get 40GB.

If the data is that important to you, go buy another 60GB drive and mirror the 60s.

The drives don't need to be the same speed, but it helps (performance-wise) if they are.

voodoosand · Sep 8, 2002, 03:51 AM

First of all, thank you for helping snerdini. If I use the stripe method, won't I be essentially turning a 40 and a 60 gb drive into an 80 gb drive? I have exactly 65 gb of songs that are on my 120 gb main drive (the one with my system on it), and I just want to make sure that I can use Retrospect or something like that to backup my mp3 folder to another disk. This is why I was going use RAID to "combine" a 60 and a 40 since I need more than 65 GB on a backup drive. It seems like I would just have to buy a larger drive if I wanted to have redundancy...? I apologize if I was not clear, but I am a little confused now about which type of RAID to use.
Do I need to use any specific controllers in the machine or certain master/slave settings on the drives?
Thank you - Nathan

Mithras · Sep 8, 2002, 07:12 AM

Here's an article which gives the basics:
Adaptec: A Quick Explanation of RAID

Essentially, in a setup like yours, you can choose between RAID Level 0 and RAID Level 1. (Apple doesn't have software support for higher-level RAID. You need specialized hardware for that)

Level 0: Striping is for performance only.

Each time you write something to disk, it sends half the data to one disk, and half to another. Each disk writes its data at the same time, so in theory the whole operation is done in half the time.

However, this is actually less safe, since now you're dependent on both drives being OK for your data to be OK. If any ONE drive fails, you lost your data.

Level 1: Mirroring is the basic RAID for safety. It's what you (think) you want.

Every time you write something, it sends it to both Drive A and Drive B. Think of it as instantaneous backup. It means that you always have TWO (or more) perfect copies of everything you write.

However, as the others said, it will offer you only 40GB, since the drives have to be exact copies of one another.

Honestly, if this already is a backup of your data from your main 120GB disk, I'd just do a regular backup to your 80GB drive. That way you still would need TWO independent drive failures for you to lose your data.

What else to do depends on how important these mp3s really are. If your livelihood depends on them, you certainly should also be backing them up onto DVD-R and putting them in your safety deposit box, or your mom's house, or anywhere else that is far away. Again, the idea is that it would then take TWO independent catastrophes (like fire, robbery, etc.) for you to lose your data.

Post back your thoughts?
mithras

ReggieX · Sep 8, 2002, 10:46 AM

You don't need to do this. Just buy another 60G drive, copy all your songs over, take it out of the machine and store it somewhere safe. If they're THAT important, you'd have them backup up on CD or DVD, not messing about with a RAID.

mrwalker · Sep 8, 2002, 11:12 AM

In windows NT, you can make a 'volume set'. This would combine the two drives which would appear to be one large one on the desktop.

You don't get the performance advantage of RAID 0, but you will get the full combined capacity of both drives.

Is there any way to do this on a mac?

snerdini · Sep 8, 2002, 11:31 AM

Ultimately, it sounds like you might need to purchase some new drives. The best way to do this would be to buy two of the largest drives you can afford, maybe 120GB drives, and mirror those.

The reason is, while you may be able to add drives to an array, it is an advanced technique, and if done wrong, could cause you to lose ALL data on ALL drives (in the array). That's why I would recommend starting out with drives that should be big enough for expansion in the future.

The other option, of course, is to add 2 more drives later, and create another array from them, if you run out of space on your current array.

RAID is the only way I know of to get realtime backup, and if this is important to you, then RAID is the option. If backing up every night would be acceptable, you could buy a large tape drive and backup to that...

snerdini · Sep 8, 2002, 11:37 AM

Originally posted by mrwalker:
In windows NT, you can make a 'volume set'. This would combine the two drives which would appear to be one large one on the desktop.

You don't get the performance advantage of RAID 0, but you will get the full combined capacity of both drives.

Is there any way to do this on a mac?

This sounds like an NT only option, but even if it isn't, what would be the advantage to using this over RAID 0? You don't get the performance gain, and you don't get redundancy. The only thing it seems to do is create one large 'virtual partition' over two drives. Even if Mac OS X could do this, I would still recommend RAID over this.

Spliffdaddy · Sep 8, 2002, 01:12 PM

Why couldn't there be a 40GB AND a 20GB partition on the 60GB disk?

The 40GB partition would become the mate for the 40GB hard drive in a striped array - while the leftover 20GB partition could be used for whatever you want.

No sense 'wasting' 20GB of disk space.

PS, In NT it's called "disk spanning" when more than one partition are used as a 'single' drive. The benefit is that you don't need matching partition sizes like you would with striping (RAID 0).