RAID-1 array for boot volume?

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Level 1

50 points

RAID-1 array for boot volume?

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.

PowerMac G5 quad Mac OS X (10.4.1)

Posted on Nov 27, 2005 4:07 AM

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Answer 1

rob_ART

Level 2

426 points

Nov 27, 2005 5:31 AM in response to qubex

You must boot from the installer DVD and use Disk Utility to set up the RAID 1 (mirror) pair. You select the two drives, click the RAID tab, and drag them to the RAID window. Specify name and type of RAID (mirrror is default).

This action will zap your current boot drive, so you'll need to back up anything you want to keep before you do this.

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Answer 2

Nov 27, 2005 5:53 AM in response to qubex

Rob is right on with the above post.

It seems like there should be an easier way without wiping the drives, but there just isnt.

You might consider just moving your home folder to the second hard drive. That would maybe give you a nice speed boost, I think. It would also protect your personal files if your whole boot disk came crashing down.

Though I am not sure how to tell OSX to look for your home folder on that second drive...

Dave

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Answer 3

Nov 27, 2005 5:55 AM in response to qubex

Disclaimer: I'm a mac newbie, but long-time unix geek.

It doesn't make much sense to me that the only way you can mirror the drive is to reinstall. What happens if you lose a mirror due to a mechanical error on one of the drives? Do you have to backup your data, shutdown, replace the drive, reinstall the OS from scratch on a newly mirrored pair, then restore your data? Sounds pretty archaic to me. Surely there is a better procedure, even if it's a command line process.

Sorry if I didn't add anything of value to the actual post.

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Answer 4

The hatter

Level 9

61,031 points

Nov 27, 2005 6:21 AM in response to qubex

A good start would be RAID + Mirror

There are sites and FAQs on RAID, and the always "data corruption gets copied to both drives."

Usually a good backup/clone, and using one drive for system, 2nd drive for data, media files, even home directory, and an emergency boot system, is preferable, along with regular backups.

G4 MDD 1.25 1.75GB UL3D 15K Atlas Mac OS X (10.4.3)

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Answer 5

Nov 27, 2005 6:22 AM in response to qubex

Hi gubex;

What do you hope to gain with having two disk as a mirrored Raid Array?

Allan

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Answer 6

qubex Author

Level 1

50 points

Nov 27, 2005 7:38 AM in response to qubex

It doesn't make any sense that you should wipe everything and start anew to create a mirrored RAID array: the whole point is that you can add in a new disk if one of the volumes fail. That is precisely what I am trying to do.

Just for the record, I did try creating a RAID array and then installing the OS onto it. The machine wouldn't boot. Holding down Option during boot and choosing either of the hard-drives wasn't successful either.

I am quite close to achieving my objective, as you can see in this screenshot:
http://homepage.mac.com/james.junghanns/raid_array.png

The only problem is that when I select "Rebuild" to actually mirror the drives, I get this error message:
http://homepage.mac.com/james.junghanns/error_message.png

Does anybody have any ideas? I know this is possible on Xserve so it must also be possible here!

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Answer 7

Nov 27, 2005 8:34 AM in response to qubex

RAID level 1 is a mirror which means Empty will become an exact copy of System. It also means that you won't get a single 500 GB disk because the RAID 1 overhead is 100%. You'll still only have 250 GB of space.

To get the single 500 GB disk you need RAID 0 (striped) or Disk Utility's concatenated disk set.

To create a RAID set run Disk Utility, choose a drive, and click the RAID tab.

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Answer 8

The hatter

Level 9

61,031 points

Nov 27, 2005 11:51 AM in response to qubex

A RAID uses different partition maps. Once you have a RAID, then you can do the things you want, but not until you properly drag the two drives into the window. Not sure how you got where you are. It does work. And you can backup a system to another drive (Firewire or something else), build the mirror, then clone/restore the volume back over.

SoftRAID 3 seems to be more robust. you can also have the mirror read from both drives to improve reading/loading of files.

Before I ever build a RAID, though, I do an erase/zero of the drives, just like XRAID or Xserve will do when you add/install a new drive, before it will be ready for use.

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Answer 9

Nov 27, 2005 12:24 PM in response to Edwin Sneller

Well, he did say he had two 500gig drives. So, in a mirror (RAID1) configuration, he'll have 500gig of raw storage.

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Answer 10

ds store

Level 7

30,855 points

Nov 27, 2005 2:04 PM in response to qubex

RAID 1 for a boot drive is about worthless, what happens when you have a bad software or OS update?

It's immediatly written to to the other drive as well.

What's better is to clone your boot drive to the other drive when you feel the need to either manually or using auto-cloning/auto backup software like Deja Vu.

This way you can set a time to do it when your away from the computer, cloning the whole drive once a week and essential folders daily for instance.

And for some reason is your primary drive dies or suffers a OS problem, simply set the clone as the startup disk and reboot, grab your files, repair or simply reverse clone the original.

It's really the best way to go.

More in my text doc here

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Answer 11

Nov 27, 2005 5:53 PM in response to qubex

Hi gubex;

I concur with DS_Store on his appreasial of Raid 1 as a system drive.

Too many people are looking at Raid 1 or mirroring as an alternative to backup which it is NOT.

My work is supporting OpenVMS servers and I don't know how many time I have had to explain to management that Raid 1 or mirroring is not a valid alternative to backup.

Allan

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Answer 12

PictorGuy

Level 2

255 points

Nov 27, 2005 6:20 PM in response to ds store

RAID 1 for a boot drive is about worthless, what
happens when you have a bad software or OS update?

If you're using RAID 1 as an alternative to backups then yes -- I would agree. However, RAID 1 is fine to use if you want to increase MTBF. Note the difference between MTBF and backups. And in some cases RAID 1 increase read times but it depends on the implementation. I'm not 100% sure of how Apple implements RAID 1 other than it's a software RAID. So there is a question of how well RAID 1 will improve read time, data transfer and reduce seek times in the Powermac.

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Answer 13

Nov 28, 2005 5:41 AM in response to Allan Eckert

And I have to disagree. If the system is an important system, mirroring the OS will minimize any system unavailability due to a hard drive failure (assuming it doesn't corrupt any data when it fails). Backups are equally important with RAID1 or without it.

However, for most desktop users RAID1 is overkill. Take frequent backups and/or clone the drive periodically so you can get back to work w/o too much downtime.

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Answer 14

ds store

Level 7

30,855 points

Nov 28, 2005 8:30 AM in response to Cuisinartoh

If the system is an important system, mirroring the OS will minimize any system unavailability due to a hard drive failure

Realistically how many people's OS's change on such a fast and constant basis that a mirror is necessary? It only takes anywhere from 20 minutes to a few hours to clone a drive and it can be set to do it automatically during the off hours.

One still has to boot from the clone or the mirror anyway to bring their system back online. So where is the time savings?

If your recording ET talking to your computer I can see having a mirror set of files drives, becasue one can't certainly ask him to repeat himself, but cloning a whole drive once a week and backing up certian vital folders daily, hourly or instantly is a better way to go.

This way one is protected in case their OS fails, gets corrupted, bad install etc.

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Answer 15

PictorGuy

Level 2

255 points

Nov 28, 2005 8:38 PM in response to ds store

Don't forget the reduced read times (I miss stated this benefit in the earlier post) and potential increased transfer rate of a RAID1 array. There are bonuses to RAID1. It's not used very often outside the enterprise but it shouldn't be overlooked.

Good basic RAID information...

http://en.wikipedia.org/wiki/Redundantarray_of_independentdisks

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