MacPro Drive Configure: Can you RAID1 to partition?

[speekez]

OK, these might be some obvious questions, but I could use some advice on drive configuration. Here's my Mac Pro setup, all internal drives:

1. 250GB - System and Apps, work files
2. 500GB - Time Machine target drive (backs up everything from 250GB)

I ordered a new 750GB from Newegg. Actually, I ordered two accidentally. I could return the extra, but wondering if I should keep it and outfit my machine as follows.


1. 250GB - System and Apps
2. Partition the 500GB into:
PARTITION A, 250GB : RAID 1 Mirror of Drive 1 (System and Apps) --
So I have a bootable exact duplicate of System drive and all Apps, that
is constantly updated. ***
PARTITION B, 250GB: Photoshop Scratch, old archive, or maybe a Windows boot

3. 750GB - All of my documents, and photography work files

4. 750GB - Time Machine target drive (backs up everything from drive 3). Using Time Machine instead of a mirrored RAID 1 here so that I have the flexibility of going back to older versions if need be.... at least when drive isn't to capacity.

*** Questions:

1. Can you run a RAID 1 using a partition. That is, can I create a RAID 1 between Drive 1 and Partition A of drive 2.
2. Do both drives need to be blank when I set up a RAID? All my System and Apps are on drive one -- will I be able to set up the RAID 1 with Partition A without having to erase it and reinstall everything?

I appreciate the guidance.

 

[hayduke]

I don't think you can RAID 1 with a partition, but someone wiser that I will give you the real low-down soon enough. Also, I think you want a dedicated drive for a scratch disk, not a partition. The role of a scratch disk is that it can spin and seek for scratch data without being interrupted by application or system needs. So this is what I would do...

1) Keep both drives...if you can afford it. They're pretty cheap these days anyways, right?
2) I would set-up the 250GB as a scratch disk.
3) I would set-up #1 750GB as a 250GB and 500GB partition.
.....A) 250GB partition is for System and Apps
.....B) 500GB partition for images/movies/data
4) Mirror or nightly back-up #1 750GB to #2 750GB
5) Use 500GB as time machine back-up for your 500GB partition.

Down the line you can buy another 750GB drive (possibly leave the 250GB drive out), make the 500GB drive a scratch drive (although you probably don't need a scratch that big) and set-up a RAID1 + Time Machine.

This all assumes that you aren't that close to filling the suggested 500GB partition with data/images/movies already and having a 500GB Time Machine drive makes sense. I haven't read what people suggest for their Time Machine drives, but it must by >100% of the primary drive.

Just my thoughts...

 

[GoodWatch]

RAID 1 on one drive just defeats the whole principle. Just like RAID 0 on two drives which isn't RAID at all. RAID 1 is a mirror over two drives, meaning that all data exists on two drives in an identical fashion. If one drive fails, you still have all data on the other drive. If one drive in a RAID 0 array fails you have... nothing. If it would be possible to trick software RAID into using two partitions on one physical drive and that drive fails you have... nothing. Just my 2 Euro cents.

 

[speekez]

RAID 1 on one drive just defeats the whole principle. Just like RAID 0 on two drives which isn't RAID at all. RAID 1 is a mirror over two drives, meaning that all data exists on two drives in an identical fashion. If one drive fails, you still have all data on the other drive. If one drive in a RAID 0 array fails you have... nothing. If it would be possible to trick software RAID into using two partitions on one physical drive and that drive fails you have... nothing. Just my 2 Euro cents.

Goodwill -- thanks, but I think you misread my post. I wasn't suggested creating a RAID1 between two partitions of the same drive. I was looking to created a RAID1 between 1 250GB drive and a 250GB partition on an entirely different drive. So, that the contents of the first drive are mirrored onto the partition. My question I guess is do RAID1's need to exist only between two drives that are not partitioned... or can a RAID1 relationship exist between one drive and a target partition on another.

The other question was if I need to wipe both drives clean to create the RAID1 mirror, as one of the drives already has all my System on it.

Hayduke -- thanks for the ideas.

 

[GoodWatch]

Goodwill -- thanks, but I think you misread my post. I wasn't suggested creating a RAID1 between two partitions of the same drive. I was looking to created a RAID1 between 1 250GB drive and a 250GB partition on an entirely different drive.

I did and I apoligize. I only have experience with RAID controllers and they build the RAID set below OS level. Warning that all data on the drives will be lost if you start. In an OS I have no experience but I can imagine that if you are dependent on the OS itself to build and maintain a RAID set that also defeats the principle: no OS, no RAID set any more.

 

[Digital Skunk]

I am sure that you can't RAID a single drive and another partition. The last time i read about RAID you couldn't do it unless it was a separate drive, but things may have changed.

 

[tyr2]

1. Can you run a RAID 1 using a partition. That is, can I create a RAID 1 between Drive 1 and Partition A of drive 2.
2. Do both drives need to be blank when I set up a RAID? All my System and Apps are on drive one -- will I be able to set up the RAID 1 with Partition A without having to erase it and reinstall everything?
.

1 - Yes that should be possible. I have my setup configured with 2 physical disks. From this I have a RAID1 for boot (using a partition on both disks) and a RAID0 (using a different partition on both disks) for scratch and other stuff I need speed with.

2 - They don't need to be blank. You can convert an existing volume to a mirror with only one member, then attach the other half of the mirror to it. This will sync the existing contents across. However you need to do this with the command line 'diskutil' rather than the disk utility gui (unless it's better in Leopard). The enableRAID and addToRAID options are what you need. 'man diskutil' should get you started.

 

[Anonymous Freak]

I can confirm that the Intel chipset supports "Matrix RAID", where you can use part of a drive for a RAID, and part separately. (Or even have two separate RAIDs; such as half of each drive in a RAID 1, and half of each drive in a RAID 0.)

But I don't believe that Mac OS X supports this. I will check when I get home on Sunday, as I'm on my MBP with no external drives at the moment.

 

[tyr2]

I can confirm that the Intel chipset supports "Matrix RAID", where you can use part of a drive for a RAID, and part separately. (Or even have two separate RAIDs; such as half of each drive in a RAID 1, and half of each drive in a RAID 0.)

But I don't believe that Mac OS X supports this. I will check when I get home on Sunday, as I'm on my MBP with no external drives at the moment.

You are correct that OS X doesn't support the onboard RAID with the intel chipset. However the software RAID works just fine for this kind of configuration (if not as quick as it would be in hardware).

Just a follow up to my earlier post. I used the whole disk + partition on a different disk, layout to migrate my old RAID volume to a new set of disks. A partition matching the current size of the existing RAID volume was added to the RAID set then the original disk was removed.