Questions - setting up a software RAID on my Mac Pro

[valdore]

I have a 2007 model 8-core Mac Pro, which I ordered with one 750 GB hard drive. Now that hard drive has less than 10% free space, and it's time to throw a second drive into my machine.

I am wanting to get a 1TB drive to supplement the original 750GB drive - will I be able to set up a mirrored RAID (RAID 1) when the two drives are of different sizes? Also, when it comes time for a third hard drive (another year maybe), will I be able to incorporate the third drive into the mirrored RAID? Or can it only be done with an even number of drives?

One more thing: are there any other RAID configurations that would be more beneficial than a mirrored RAID? My Mac Pro is a photography computer, and offhand I thought the mirrored raid would be ideal in case of a hard drive failure to save all the photos...

Please advise.

 

[Toups]

You can setup a mirrored RAID of 2 drives of different size, but you will only be able to RAID to a max of the smaller of the two.

I you plan to use 3 drives, you can use RAID 0 which will stripe the data and make all of the space available or use RAID 5 and have 2x the space of the smallest drive available, the rest will be lost to data parity.

Keep in mind you will still need a drive for the OS, and if that drive fails you could potentially lose ALL of the data on the array.

 

[valdore]

Thanks for the reply. I thought though that this thread would garner a lot more responses.

I have another question: Since my one drive is 750 GB, if I buy another 750 GB drive and set up a mirrored RAID, I won't actually gain any more storage capacity at all, will I? Since the one current drive is 90% full, then that would make the 2nd 750 GB drive that full as well wouldn't it? ...so I guess by mathmatics if both had ten percent free space then I actually would have a meager 10 or 20% storage increase for the whole array? (sorry, i'm terrible at math).

 

[lancestraz]

Thanks for the reply. I thought though that this thread would garner a lot more responses.

I have another question: Since my one drive is 750 GB, if I buy another 750 GB drive and set up a mirrored RAID, I won't actually gain any more storage capacity at all, will I? Since the one current drive is 90% full, then that would make the 2nd 750 GB drive that full as well wouldn't it? ...so I guess by mathmatics if both had ten percent free space then I actually would have a meager 10 or 20% storage increase for the whole array? (sorry, i'm terrible at math).

You would still have only 10% free space. But you would have a backup if one of your drives broke.
If you want to increase capacity don't do RAID 1. Use RAID 0.
If you want a "up to the last second" backup, use RAID 1.

I have a question though....
Can the Mac Pro set up an array of hard drives in RAID 0 without purchasing a dedicated RAID card and without suffering a major hit in performance?

 

[valdore]

I have a question though....
Can the Mac Pro set up an array of hard drives in RAID 0 without purchasing a dedicated RAID card and without suffering a major hit in performance?

The Mac Pro can run software raids for RAID 0, RAID 1, and a concatenated array (technically not a RAID).

Further questioning from me:

-Is it true that there is no point in having a RAID 1 (mirror) if you have three or more drives? (for some reason I had been under the impression until recently that you could still have a RAID 1 but with multiple drives, AND increased storage capacity.

-Is it possible to have a RAID 0 using different sized drives, or do they all have to be the same too? (I ask because in reading about concatenated arrays, it said it gives an advantage over RAID 0 in that different sized drives could be used...)

 

[lancestraz]

-Is it true that there is no point in having a RAID 1 (mirror) if you have three or more drives? (for some reason I had been under the impression until recently that you could still have a RAID 1 but with multiple drives, AND increased storage capacity.

I think that's called RAID 0+1 or something....

-Is it possible to have a RAID 0 using different sized drives, or do they all have to be the same too? (I ask because in reading about concatenated arrays, it said it gives an advantage over RAID 0 in that different sized drives could be used...)

You can but the max size will be limited to the smallest hard drive*2. e.g.
HDD 1 = 100GB
HDD 2 = 100GB
Total size when placed in RAID 0 = 200GB.

HDD 1 = 100GB
HDD 2 = 175GB
Total size when placed in RAID 0 = 200GB. So you would be wasting 75GB.

Wikipedia RAID page.

 

[valdore]

If I get a hardware RAID controller, set up a RAID 0+1, with four drives at 750GB each, how much storage total will I have?

 

[lancestraz]

If I get a hardware RAID controller, set up a RAID 0+1, with four drives at 750GB each, how much storage total will I have?

3 terabytes of total storage, but 1.5 terabytes of storage you can use. The other 1.5 will be the backup.

So you'll have...
750 GB
---------)-- 1.5 TB of space to put whatever on. RAID 0.
750 GB

You'll also have...
750 GB
---------)-- 1.5 TB of space that will be a constant backup of the two above drives. RAID 1
750 GB

 

[valdore]

1.5 terabytes.

Thanks for the quick reply.

1.5 Tb... that sucks. I'm finding RAID not very accommodating; with no mirroring I statistically increase my chances of losing everything if one hard drive fails, or mirroring and not having nearly enough long term storage for the life of my Mac Pro.

 

[kakace]

Why don't you consider RAID 5 then ?

 

[valdore]

Why don't you consider RAID 5 then ?

Ah I forgot momentarily about that.

I can't find any good info on the net - if I have three drives at 750 GB each, how much storage will a RAID 5 give me? There is redundancy with RAID 5, isn't there?

 

[mrcandy]

Ah I forgot momentarily about that.

I can't find any good info on the net - if I have three drives at 750 GB each, how much storage will a RAID 5 give me? There is redundancy with RAID 5, isn't there?

A RAID 5 provides redundancy spread across all drives in the array. The array will continue to work with no loss of data with one drive failed. A minimum of three drives is required, each of the same size. Available capacity is size of one drive multiplied by (number of drives in array - 1).

If you put 3 x 750GB drives into a RAID 5 you will have 2 x 750Gb = 1.5 TB available capacity with redundancy for a single drive failure.

Note that RAID 5 requires a hardware RAID card, there is no software support for RAID 5 in OSX.