Setting up RAID 1

[rajeevmac]

I have never setup RAID before and this question may be totally stupid for that matter.

Can I setup RAID 1 (or call it mirroring) without the RAID card? I have two 1TB internal drives in my Mac Pro and I want to mirror them. I don't want to spend another 700 bucks just to setup a mirror.

Disk Utility shows some RAID options, but I am not sure how to use them, or if they will work at all without the RAID card.

Thanks,
Raj

 

[trainguy77]

Yes they will work without the RAID card it just means that the CPU does the work instead of the card.

 

[Tesselator]

RIAD 1 is no speed advantage at all tho. RAID 0 is the one that speeds things up.

Anyway, TrainGuy said, yes - you can do either (and a combination of both (0+1 and 10) without a dedicated card. I just wanted to add that the amount of CPU usage it requires is so small that it's not actually even measurable.

 

[trainguy77]

RIAD 1 is no speed advantage at all tho. RAID 0 is the one that speeds things up.

Anyway, TrainGuy said, yes - you can do either (and a combination of both (0+1 and 10) without a dedicated card. I just wanted to add that the amount of CPU usage it requires is so small that it's not actually even measurable.

Thats not true in RAID 1 your read speeds increase compared to a single disk.

 

[Tesselator]

Thats not true in RAID 1 your read speeds increase compared to a single disk.

Mmm, no, not really. If you have more than one app reading at the same time then it can be just a hair faster. It will always be slower at writing. But single threaded reads like loading applications and app doccuments (video, images, etc.) AFAIK show no improvement at all. None - zero - zip - nada.

Wiki says basically the same thing:

RAID 1

'Mirrored set without parity' or 'Mirroring'. Provides fault tolerance from disk errors and failure of all but one of the drives. Increased read performance occurs when using a multi-threaded operating system that supports split seeks, very small performance reduction when writing. Array continues to operate so long as at least one drive is functioning. Using RAID 1 with a separate controller for each disk is sometimes called duplexing.​

 

[nanofrog]

Thats not true in RAID 1 your read speeds increase compared to a single disk.

What kind of usage have you seen this happen with?

I've never really noticed it (if it ever occurred), but any software company willing to write code that can, would be worth noting.

 

[trainguy77]

http://blogs.zdnet.com/Ou/?p=484 It also has more benchmarks on page 3. its a small increase. But still an increase. Especially for a server environment. Plus you get the benefits of it being a mirror, which should be the primary reason to going with RAID 1.

 

[Tesselator]

Yeah, that looks about right:

Single = 64 MB/s Read 64 MB/s Write
RAID 1 = 73 MB/s Read 73 MB/s Write
RAID 5 = 218 MB/s Read 193 MB/s Write

And RAID 0 should profile very much like RAID 5 but a little faster and without the CPU hit. (all other things being equal)

But I don't believe their results are completely accurate. Write performance should be worse than single drive, not better. So I think they messed up their tests! Maybe they're profiling the difference in double drive caches as opposed to the size of the cache on a single drive or something.

But also to consider is that there really isn't a call for hardware level backup in desktop systems. Remember RAID 1 is NOT a replacement for a software backup. It you lose a file or a bunch of files due to almost anything that's likely to occur then it's lost totally in a RAID 1 system just as for a single drive. For this reason you have to keep a software backup anyway. RAID 1 will only save you in the off chance that one drive breaks or stops working completely and additionally doesn't take the other drive(s) or the files on them, with it. If you keep a backup as you would even with a RAID 1 then you don't really need a hardware duplication level like that. The only time you would want this is when it's critically important to have the data back on-line within seconds after the disaster. If you don't mind waiting an hour or so then there's no reason at all to have RAID 1.

 

[nanofrog]

http://blogs.zdnet.com/Ou/?p=484 It also has more benchmarks on page 3. its a small increase. But still an increase. Especially for a server environment. Plus you get the benefits of it being a mirror, which should be the primary reason to going with RAID 1.

Thanks for the link. I'd about given up on ZDnet.

I would expect any software that can, would be meant for a server. Perhaps the occasional workstation, but not common.

I do wish they'd tested against other controllers, particularly Atto, Areca, Adaptec,... (well known at least), set up for maximum throughput (write back = enabled), and gone to a larger Q depth. My interests.

My own testing with an ICH10R on an i7/W35xx workstation board is sort of dissapointing. It couldn't even let a 4 drive stripe (64K) exceed 156.6MB/s on average. Given the simplicity, and the drives used, (WD3202ABYS)*, I'd have hoped for a little more.

*Tested at 97MB/s as a single drive on the same controller.

 

[Flash SWT]

Rajeevmac, yes you will need to configure the RAID 1 through Disk Utility. You can do it will booted if you are using two drives that do not have OS X installed on them. I'm pretty sure it will erase both drives during the setup so make sure you don't have any data on them. (There is a way around this using Terminal if you really can't backup the two drives first.)

If you want to create the RAID mirror for your OS X drive you'll need to boot off the install CD and run Disk Utility from there to create the mirror then reinstall OS X.