RAID-1 (mirrored) for boot volume?

[qubex]

Hello.

I have a new quad-G5 with 2x500GB HD. One disk is "System" (with all the system and user data on it, applications etc.) and the other one is "Empty" (nothing on it).

I want to set up a RAID-1 (mirrored) array, so that System's contents are mirrored onto Empty and appear as a single 500 GB disk.

I've been reading what little documentation exists but I really can't figure out how to do it. Can somebody explain exactly how I go about mirroring the boot drive?

Much obliged for your kindness.

 

[trainguy77]

First you need to decide if you are going to use hardware or software. Software will use your CPU. Hardware uses your RAID card. So it depends if you want to spend some cash.

 

[CanadaRAM]

Hello.

I have a new quad-G5 with 2x500GB HD. One disk is "System" (with all the system and user data on it, applications etc.) and the other one is "Empty" (nothing on it).

I want to set up a RAID-1 (mirrored) array, so that System's contents are mirrored onto Empty and appear as a single 500 GB disk.

I've been reading what little documentation exists but I really can't figure out how to do it. Can somebody explain exactly how I go about mirroring the boot drive?

Much obliged for your kindness.

One thing to check first -- why do you want to do this?

A RAID is not a backup -- if you have a crash and corrupt a System file, or if you accidentally delete something, or if you overwrite a good file with a bad one of the same name, your mirror is equally as @%$@^ed as your primary. A RAID is good only in the event you have a catastrophic hardware failure of one drive.

A mirror is best in situations where you have transactional data that changes minute by minute, and you can't tolerate even a few hours of lost data.

I would suggest looking at cloning your boot drive, and then setting up a periodic backup or sync strategy with some software.

 

[MacsRgr8]

Good thing to be absolutely sure why you want this RAID solution, but once you have chosen this, it is very easy to do.

Default Mac OS X software RAID 1:
* YOU MUST REFORMAT THE CONTENTS OF THE HD *
- Boot from DVD, and Start Disk Utility
- Select a HD
- Select RAID, and configure it from there!

That's the easiest way to do it.

It really is drag & drop, WYSIWYG.. i.e. the "Apple" way of doing it, once you have booted from the install DVD, and opened Disk Utility.

 

[qubex]

Right, lets start off from the beginning.

I ordered 2x 250 GB HDs. Apple accidentally shipped me 2x 500 GB, and of course I'm not complaining, but I don't really know what to do with twice the storage.

I figured I'd try RAID1 because I wanted to boost read performance. I thought about RAID0, which theoretically can boost read/write performance, but then I changed my mind because that's simply too risky. I'll be using software because I really don't want to spend the money for another card when I have 4 G5 cores available to crunch a bit of data... it's RAID5 that causes a heavy computational load, anyway. By comparison, RAID1 is very circumspect in its requirements.

Anyway, I spent two days on the line with Apple Tech support trying to create a viable RAID1 array from within Disk Utility on the OS X install CD. It just wouldn't work - I received continual messages that the array specified was invalid, or that it could not update volume headers, etc. etc. Basically it didn't work at all.

So I was looking for somebody who had actually done this before, and I wanted to know how you'd done it: specifically how did you tame the Disk Utility beast?

 

[Makosuke]

I figured I'd try RAID1 because I wanted to boost read performance.

Are you sure you're going to get this from Disk Utility's RAID1? So far as I know (at least the last time I checked) Apple's RAID1 implementation doesn't do a thing for read performance--it's just a straight mirror. Has this changed with Tiger?

I've set a similar array up to what you're talking about, but I used SoftRAID, which is not free (it does, however, use both disks to improve read performance). In that case it was extremely easy, but it won't apply to you, so I apologize that I can't be of any help.

Were I in your shoes, I'd do one (or both) of two things:

1) To boost performance, just work off of one drive and use the other for your OS. It's a huge waste of space if you don't have many files, but it'll significantly increase both read and write performance if you're doing anything disk-intensive while the OS is accessing the disk.

2) For security, do what's been suggested by others--set up an automated nightly backup to the 2nd drive.

3) Do both: Partition the non-boot drive into two chunks, use the first partition for high-speed data access, and the 2nd one as a nightly mirror of your boot drive. This is what I do--that way if my OS drive dies, I've got a ready-to-run backup from the night before, but since my boot drive isn't nearly as big as the whole thing I use the rest of the backup drive for nonessential files, which is faster than running everything off the boot drive.

 

[qubex]

Thanks for the suggestions!

I'm currently using one disk for backup/VM and the other disk as my main system/applications/data disk. I'll probably move my applications and large user data to the second drive.

As for RAID1, it's come to the point where I really can't be bothered.