View Full Version : RAID on Steroids

09-26-2001, 11:33 PM
I have just discovered a new speed concept that blows my mind. I am curious if anyone has heard of this configuration and or actually set one up.

I am setting up one of my Dual 800's to be a file server, so naturally I will be attaching a big fast RAID to serve the files. Since I need mega space I am planning on 2 Hardware RAIDS each hooked up to its own bus.

So what, big deal 2 RAIDs thats not exactly mind blowing. Its kinda pigish but not mind blowing.

Well here is the mind blowing part.

Since both RAIDs are hardware based, they will appear as 2 seperate single volumes to my Mac. So that means I can stripe the 2 RAIDs together with OS X's built-in software based RAID drivers and Whamo!! I have a RAIDed pair of RAIDs

Forgive me but I must http://www.macgurus.com/ubb/dance.gif

09-26-2001, 11:51 PM
FT, you scare me man. Have you considered professional help?


09-27-2001, 02:17 AM
Sorry¨÷ There's a flaw to your logic. While each RAID would appear to an OS as two volumes, the hardware still appears as 4 devices to the drivers.

09-27-2001, 01:28 PM
Since when would failed logic stop me?

What I am proposing doing is called RAID 50 or sometimes known as RAID 5+0. The way I understand it the 2 hardware RIAD would be set to run RAID level 5. They would be striped by OS X's software.

If this really is not possible could you please elaborate on why not. I will never claim to understand all of this. I have read alittle on RAID 5 + 0 and it seems possible to me.

The proposed RAID's will consist of 6 drives each with a hardware RAID controler. I believe the goal is to stripe them RAID 5. Since these are hardware RAID controllers they will show up as single id on one SCSI bus and another single id on a different SCSI bus. The OS will not know that they are RAID's. They will look like 2 really big drives. Then the OS will stripe the drives at RAID 0. This configuration is known as RAID 50 or RAID 5 +0.

I am going to get it in writing that it will work before I sign the P.O.

Please let me know if this really is not possible.


09-27-2001, 06:23 PM
The OS doesn't do the striping. The Driver software does. Since you're using two different driver programs doesn't change the fact. You could likely do a Striped & Mirrored RAID with the array but only one driver can be used for the entire setup.

09-27-2001, 09:15 PM
[b]Since when would failed logic stop me?/b]
I think you have been reading way to much Hitchhicker's Guide to the Galaxy http://macgurus.com/infopop/emoticons/icon_wink.gif

A RAID 5+0 makes no sense in my experience. There are (that I know of)
RAID 0 (stripe: 2 drives min)
RAID 1 (mirror: 2 drives min)
RAID 0 + 1 (mirroring a stripe: 4 drives min)
RAID 5 (similar to RAID 0+1, but overall more efficient and probably needed a hardware controller: 3 drives min)

RAID 0 gives you 1xadditional drives increase in speed (theory) and size (reality) you also lose reliability - in theory.

RAID 1 give you 2x reliabilty and 1/2x the size, write speeds would be about the same for a single drive, but read speeds can be a bit faster.

RAID 0+1 gives you all the speed and size of the fastest RAIDs but also allows you to mirror this - so you still loose 1/2 your total drive space.

RAID 5 is a nice mix - you only loose 1/3 of your drive space and you gain in speed & size - but because it is more complext you (IMO) REALLY need a hardware controller that understands and handles this well - and of course this would need to be supported by the system software.

Classic Mac OS has no (good) support for complex RAIDs. It will only work with RAID 0 or RAID 1 and newer system will not (normally ) boot from a RAID 0 volume and I have heard there can be issues booting from a mirrored volume as well. All this is done in software too... and it works pretty nice in my experience. It kinda gives those old, small & slow SCSI drives new life! http://macgurus.com/infopop/emoticons/icon_smile.gif

I know 10.1 has some support for RAIDs, but I do not have this yet. I would guess that with the unix BSD roots of X you might be able to get something reliable. There has (I guess) been time for vendor to actually test their hardware on a realworld Mac running X or X Server ... or maybe not. Often hardware RAIDs must pass much more rigid tests than consumer wares. Of course that is probably why they cost more?

I would bet 10.1 only supports software based RAIDs and it probably does not even support booting from them, but if I'm wrong - so much the better. I am really not sure how you got this hardware RAID notion into your head

You can do this with SCSI or IDE/ATA, but SCSI is the way to go for the best performance. Of course if its not a money making/time saving /$$ earning system - then maybe IDE/ATA is the best?

Strangley I was showing a new guy at work the wonders of SCSI and RAIDing today. http://www.macgurus.com/ubb/eek.gif

One Nation, under God; with liberty and justice for all.

09-27-2001, 10:34 PM
I have confirmed that it is possible to do RAID 50 with Mac OS X server. This is possible because the RAID controlers are what the Mac will see. The Mac is not mounting the drives directly. The Mac will see the pair of RAID controlers and allow me to create a new 0 stripe.

Now if this blows up in my face I will let everyone know and then imiediatly ask to be demoted back to Junior member status and summarily be jeered by the group. Of course if this does work I will let you know as well. That is as soon as I get done celebrating.

I am about to upgrade our entire production area with new Macs and network.The Mac OS server that is proposed to have this 900GB RAID 50 will be connected to the network with dual fiber channel cards. This thing should be big and fast.

BTW dragon, this wacked idea was just one of those what if kind of thoughts I had while cutting my lawn. I have not read The Hitchhikers guide to the galaxy yet. Maybe I should.


There is more room to think outside the box.

09-30-2001, 09:22 PM
I have completed jumping through all of my companies hoops http://macgurus.com/infopop/emoticons/icon_biggrin.gif:

Speed, its only a matter of time now!!

10-01-2001, 02:57 AM
FT, definetly read Hitcher's Guide to the Galaxy, it'll suit you well!!!!


"I made a conscience decision in a semi-conscience state"

10-01-2001, 08:38 AM
X and X Server have BSD roots - so I could see it supporting a hardware RAID 5. I still do not understand what RAID 5+0 or RAID 50 - it seems kind of reduntant.

RAID 5 + Tape backup seems a better solution.

10-01-2001, 12:41 PM
I will be doing tape back up with a 7 tape library LTO unit from ADIC and Retrospect. I was not all that familiar with LTO before I started working out specs my new Mac workstations and server. LTO is very fast and capable of holding 200GB per tape. I have seen real world back ups running at over 1GB per minute. So I am planning on doing on tape back-up. This of course is the least cool piece of technology that will be part of my new system.

There are 2 main reasons I am planning on the RAID 5+0.
1) Striping the 2 450GB RAID5 units together will result in on Mammoth drive on the server. It will be much easier to manage 1 huge drive rather than 2 unique volumes in a very collabrative work enviorment.

2) Speed. RAID5 is fast and has built in parity. That means if on of my 6 drives in either of the RAID boxes fail, the system keep runniing off the parity data. I get a warning and pull the bad drive, replace it with a cold spare that I have on hand. The RAID rebuilds the new drive as a replica of the one that went bad. All the while production keeps working like nothing happened.

Striping the 2 RAID5 units as RAID 0 is well just a way to add speed. That is of course the reason we all love RAID 0.

When my wife asks me. http://www.macgurus.com/ubb/eek.gif " Why I have to go that fast?"
I always answer, http://macgurus.com/infopop/emoticons/icon_biggrin.gif " It doesn't go any faster."


10-01-2001, 01:34 PM
interesting idea--definitely let us know what happens!

I, for one, will never jeer.

the only way to find out if something will really work is to try it.


10-04-2001, 01:16 PM
This sounds possible

As I understand scsi These hardware controllers must be using the Logical Unit Numbers (LUN's) that have been part of the scsi spec for many years LUN's allow you to have (on a narrow bus) 7 hardware devices per scsi ID # ( scsi ID 1:1 ID 1:2 ID 1:3 etc) OS 9's drive setup still displays LUN #'s I believe.

Anyway In the past you had to have a hardware device to assign the ID # to then that device distributed the LUN #'s The whole mess was seen as one device You could format the individual drives seperately but they were treated as multiple partitions of the same device (I believe)

IF this is the case here I think that OS X could stripe 2 hardware raids together in a software raid stripe

I do not think you will see the ungodly performance that this setup would imply though. IF it works you will quickly reach the top end of your bus speed ...which you could do with an ATTO and 4 x15's in a Softraid 2 channel stripe

10-04-2001, 07:40 PM
I'm a bit confused. What hardware raid are you using that works in the mac os?
I thought the only raid solutions avaliable for a mac, are software raids???



10-04-2001, 07:41 PM
When did someone start making hardware raid controllers for macs????


10-05-2001, 12:58 PM
Hello Santilli,

Good questions.
What hardware raid are you using that works in the mac os?
I thought the only raid solutions avaliable for a mac, are software raids???

I would be happy to share this info with you, but out of respect for our Mac Guru hosts I would like permission from them to openly discuss this topic. I greatly appreciate this site and all of its support. The MacGurus are great and valuable resource for the Mac community. The solution I have found is with a RAID manufacturer who's RAIDs are not available through MacGurus ......yet.

I know that this is a pretty open forum but I still would like to have permission to speak openly.

Mac Gurus is it ok to mention a specific RAID manufacturer?


10-06-2001, 10:40 AM

I took a day off and magician is probably building something in the basement. Speak. If I recall correctly, he has tried some already. k

10-10-2001, 03:27 PM
There are several hardware RAIDs available from a company called Rorke Data. The RAIDs are available as Fiber channel, Ultra 160 SCSI and IDE/LVD. I have eliminated the fiber channnel solution from my plans due to cost and driver problems with OS X. The Galaxy 10 RAID is an Ultra160 scsi RAID with great scalabilty and redunant controlers. I of course am going with the more out of the box solution, the Galaxy i. The Galaxy i is an IDE to LVD RAID solution. The drives are IDE but there is an Ultra160 bridge. The specs of this unit are very impressive. I am installing 2 units that will be striped together to create my RAID 50 system.
I would prattle on about the specs but the following web page will do a much better job.

When I began looking for a server RAID solution I was initially looking for a hardware RAID. The software RAIDs that are being built really seem to fit the needs of most situations. I am putting in x15 cheetahs in my Mac workstaions. Many thanks to everyone and the Gurus for helping me research this wild technological area. I still plan to test ATTO vs Softraid to verify which will work best for my workflow. The two Galaxy i's are going to be striped as a large file server connected to a Mac OS X server all of which will all be connected via dual fiberchannels to an extreme network GB switch.


10-10-2001, 09:06 PM
Just curiosity, but is the data protection when you stripe a couple of raid 5s just as good as just the plain Raid5? It gets a little complicated figuring out the logics of your array, and I couldn't help wondering.


10-11-2001, 08:34 AM

Yes, the RAID 5 protection of this solution is the same as a stand alone RAID 5.

Here is a recap of this solution.

2 Hardware RAID's both setup as RAID 5.
OSX server striping the RAID's as RAID 0.

RAID-5 + RAID-0 = RAID 5+0 or RAID-50

Since the two RAID-5 units are independent of the OS X server they benefit from all of the normal RAID-5 protection. This means if one of my individual drives of either of the RAID-5 units were to fail the unit would continue to run from parity data.

I have a cold spare drive for each of the RAID's that will be used to replace a failed drive and rebuilt from the parity data. It may be possible to run with parity data, but I would'nt want to do that any longer than it will take to slap a cold spare in and wait for the new drive to be rebuilt.

I got a call yesterday and it looks like my hardware will all be ready for integration within a week.
Its time to put the plan in motion!!!!!! http://www.macgurus.com/ubb/dance.gif


[This message has been edited by FrozenTundra (edited 11 October 2001).]

10-15-2001, 09:31 PM
Thanks, learn something new everyday.

Keep us posted on the results.


10-20-2001, 05:50 AM
Actually you do have lower reliability, but it's probably not enough to worry about.

A normal RAID 0 has a higher statistical failure rate than using a single disk to store the same data simply because there are now multiple disks which can fail, and it is only necessary for one of them fail for data loss to occur. 2-disk RAID 0 = twice the failure rate of a single disk, so on and so forth.

This doesn't change when the RAID-0 stripes are RAID-5s instead of single disks. A RAID-5 array has a nonzero probability of data loss (requires two or more disks to fail at the same time, or close enough that rebuilding the first failed disk hasn't completed when the second fails). This is a fairly low probability event, or it wouldn't be terribly worthwhile to use RAID-5, but can happen.

So, by striping two identical RAID-5s together, you are doubling the chance of losing data when using a single RAID-5 of the same configuration. Since that's pretty unlikely to begin with, barring nasty events like a power supply failing and taking multiple drives with it, two times unlikely is still way down there, and there isn't much to worry about.

11-15-2001, 01:25 AM
I don't really worry about losing data. While I know that a drive will fail at some point, it will not take me down.

Two words, religous back-ups.