[Jupeman]

I have searched these forums. I have read posts on MacGuru. If I missed the answer to this question in those forums, please direct me. Otherwise here goes my question:

When I take delivery of my 2Ghz dualie G5 sometime (soon), I'd like to set up a RAID right away. My primary concern is data protection, thus I am thinking of running two internal 250GB drives and mirroring. The question is, will this work?

1) Can I boot off a mirrored setup?
2) Would it be better to buy a fast boot drive (some sweet 10k rpm thing) and then mirror my internal 250GB with an external 250GB. Will this work? What happens if I take my machine somewhere without the external drive?

Either way I plan to use OS X's built in RAID-ability.

[CatOne]

Originally posted by Jupeman:
I have searched these forums. I have read posts on MacGuru. If I missed the answer to this question in those forums, please direct me. Otherwise here goes my question:

When I take delivery of my 2Ghz dualie G5 sometime (soon), I'd like to set up a RAID right away. My primary concern is data protection, thus I am thinking of running two internal 250GB drives and mirroring. The question is, will this work?

1) Can I boot off a mirrored setup?
2) Would it be better to buy a fast boot drive (some sweet 10k rpm thing) and then mirror my internal 250GB with an external 250GB. Will this work? What happens if I take my machine somewhere without the external drive?

Either way I plan to use OS X's built in RAID-ability.

Yes you can boot off a mirrored setup.

And No, no way I'd recommend you mirror to an external drive. That's ludicrous.

You're not going to get THAT much more speed by booting off a 10K drive. When you get a VERY fast boot drive, you'll note that about 75%+ of the boot time is in the firmware... where you see the grey screen with the apple logo. Once it flips to the blue screen with a fast disk it takes about 3 seconds to load the rest, but on my laptop that screen takes 10 seconds. So you go from 20 seconds + 10 seconds to 20 seconds + 3 seconds, or 30 seconds down to 23. Not significant enough IMO.

Just mirror the two internal drives, and call it good. Of course, this will mean an OS reinstall.

[Jupeman]

Actually I think my boot speed on my 1.42 Dualie is pretty fast. Also, frankly, I don't reboot very much (mmm, OS X).

Yes, I figured I'd need an OS reinstall when mirroring. I guess I don't understand the sequence required to do this. I receive the machine with OS installed. I install new drive. I say "make mirror". Then what? Do I boot the machine from the CD and mirror from there?

Also, will I lose anything reinstalling from the system disks that I assume Apple will give me. I suppose I will just backup whatever interesting "other" apps Apple hands out (such as Graphic Converter which was in a new machine bundle etc...).

[11011001]

Originally posted by Jupeman:
Actually I think my boot speed on my 1.42 Dualie is pretty fast. Also, frankly, I don't reboot very much (mmm, OS X).

Yes, I figured I'd need an OS reinstall when mirroring. I guess I don't understand the sequence required to do this. I receive the machine with OS installed. I install new drive. I say "make mirror". Then what? Do I boot the machine from the CD and mirror from there?

Also, will I lose anything reinstalling from the system disks that I assume Apple will give me. I suppose I will just backup whatever interesting "other" apps Apple hands out (such as Graphic Converter which was in a new machine bundle etc...).

No.. it's more like you get the new machine.. play with it a bit, then stick in the OS X install disk, reboot off that, once it's loaded fire up the disk utility under the Apple, go to the RAID tab, choose mirror in the pulldown thingy, choose your disks.. click ok or whatever, go back to the install screen and put OS X on there. That's about it.

Not sure if you have to reinstall with software mirroring with RAID though???? I use hardware based RAID 0 (striping), never tried mirroring.

[tadd]

Striping means that your data is distributed over multiple drives in such a way that your total amount of drive space is very nearly equal to the total capacity of the drives. Striping takes or puts data from all or both drives so that all drives are busy at the same time and you get throughput that is (theoretically) nearly the multiple of number of drives times the throughput of a single drive. Striping is dangerous in that if any drive in the striped array were to get a data error, the data error would affect the entire band of data, i.e. multiplied by the number of drives. If one of the drives were to fail, you'd lose all of the data on all of the drives. Striping is good for people who are meticulous about backing of their data to an out-of-box storage system, i.e. tape or other HDs.

Mirroring is for people who want their data protected and don't mind the loss of performance required to maintain the mirror. Mirrored performance is nearly the same as a single drive if the mirror is done across separate busses (as in, dual interfaces for 2 drives). Mirroring takes two drives (or sets of drives!) and duplicates the data across both drives. In a good RAID subsystem if a single drive fails, your data is still available and the insertion of a replacement drive in place of the broken unit will result in a fully restored mirror, eventually, while allowing continuous access to the data during the rebuild.

Most people who use Mirroring successfully will also use what is called an "enclosure". This is a box that holds the drives and which maintains status LEDs and signals to and from the RAID controller hardware (or host computer). The host computer or controller will signal to the user via the enclosure lights as to the status of the drives. If a drive becomes corrupted or if the array is damaged and needs or is in the progress of rebuilding, the LEDs will signal.

Look up SAF-TE on the web for more info on enclosures.

I don't know what OSX does in the case of a drive failure. It'll be interesting to find out.

There are additional forms of RAID that are even more interesting. RAID 5 is a good one.

I recommend this article: for more information
Skinny on RAID: ArsTechnica for more good reading.