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RAID and the Mac Pro

L

LightMast

macrumors regular
Original poster
Apr 16, 2007
126
0
You guys have been damn helpful so far, thanks for the assistance......but now I have another question.

Could someone help me understand the advantages and disadvantages of the various RAID versions the mac pro supports? The wili article cleared things up a bit, but I'm still a little gray on the dual setups (0+1 etc).

THanks!
 
Here's a quick overview:

Raid1=2 drives, each with exact same information. Very slight performance decrease from non-raid, if 1 drive fails, you lose nothing. You get half the total storage capacity.

Raid0=2 drives, half your data on one, half on the other. Faster performance but if 1 drive fails, all data lost. You get half the total storage capacity.

Raid0+1=4 drives, drive 1-2 are in Raid0, but drives 3-4 are copies of 1-2 (raid1). Faster performance and if 1 drive fails you lose nothing. You get 1/4 of the total storage capacity.

There are other raid varieties, namely 5, but the mac pro does not support them.
 
Danksi said:
Not 1/2.

RAID0 = Total storage of both drives added together

i.e 500GB+500GB = 1TB in RAID0
Click to expand...

Yup, copied and pasted from raid1 too quickly there. You get the capacity of your drives added, unlike raid1, but you get no redundancy and double the chance of failure.
 
janey said:
Um no, there's over a dozen raid levels.
Click to expand...

I meant raid 5. And truthfully, when not considering combinations, there are 7 standard widely used and named raid implementations.

Raid 0, 1 and 5 are the only truly widely used implementations. 2,3+4 will never be popular, while 6 is very similar to 5 but requires at least 4 drives and will become more widespread as larger drives become the norm.

All other raid implementations are combinations (I think they're called 'nested' when you combine them) such as 0+1, 1+0, 5+1 etc.

raid5 would be useful in the mac pro but Apple only uses software raid, which sucks up some processing power, and raid5 would use too much. Apple chose to disable the onboard raid controller which could have powered raid5 on intel's mobo for some reason, so an external device would be needed.
 
I've got 2x250GB disks and a recently added 500GB - I'm thinking to RAID0 the 250's together for my applications, purely to bring about a performance boost.

Is it worth the effort or would I be better-off investing in a Raptor instead and keeping the 250's for more data and/or backups?

Cheers
Dave
 
volvoben said:
Here's a quick overview:

There are other raid varieties, namely 5, but the mac pro does not support them.
Click to expand...

Actually, it does. You just need a RAID controller card, such as those by Highpoint or Areca.
 
I can't believe Apple can't do it in software... I use an Infrant Desktop NAS device with Raid-5 and I can't believe the chip in that thing is more powerful than what the MacPro could deliver...

Cliff.
 
Lycanthrope said:
I've got 2x250GB disks and a recently added 500GB - I'm thinking to RAID0 the 250's together for my applications, purely to bring about a performance boost.

Is it worth the effort or would I be better-off investing in a Raptor instead and keeping the 250's for more data and/or backups?

Cheers
Dave
Click to expand...

RAID 0 more than doubles your chance of losing everything. If anything goes wrong all the "performance boost" you had is turned into a nightmare of lost, non-recoverable files. By the time you protect yourself with a powerful enough backup system you might as well go to RAID 5 which is fast and stable.
 
Sherman Homan said:
RAID 0 more than doubles your chance of losing everything. If anything goes wrong all the "performance boost" you had is turned into a nightmare of lost, non-recoverable files. By the time you protect yourself with a powerful enough backup system you might as well go to RAID 5 which is fast and stable.
Click to expand...

How does it "more" than double it?

The speed will not increase the chances of drive failure.

The merely doubles, nothing more.

I have 2 RAID-0's in my computer alone. I just setup a 4 drive RAID-0 for my Dad (he already has a 3-drive RAID-0).
 
slughead said:
How does it "more" than double it?

The speed will not increase the chances of drive failure.

The merely doubles, nothing more.

I have 2 RAID-0's in my computer alone. I just setup a 4 drive RAID-0 for my Dad (he already has a 3-drive RAID-0).
Click to expand...

I suppose the failure rates are pretty close to the integer number of drives you have set up in RAID 0. So you have two sets of drives that are each 2x more likely to fail than my non RAID 0 drive, and your poor dad's set-up is 4x likely to fail. You guys live on the edge!!!!
 
Sherman Homan said:
RAID 0 more than doubles your chance of losing everything. If anything goes wrong all the "performance boost" you had is turned into a nightmare of lost, non-recoverable files. By the time you protect yourself with a powerful enough backup system you might as well go to RAID 5 which is fast and stable.
Click to expand...



I don't understand your logic here.

If I set up a RAID0, and have my data backed up to an external drive every night, I really don't see the risk. If I lose a drive, I just replace it and restore the data. And if I didn't have a RAID0... if I lose a drive, I just replace it and restore the data.

Everyone talks about how "if you lose a drive, you lose it all!!!"... what does that matter if it's backed up daily? Especially considering I'm using the same physical drive, it's going to fail in a RAID0, or it's going to fail on it's own. Having 2 drives in 1 array doubles my probability, but that's different than chances. I've had drives go 5 years strong and still haven't failed, lost after they were backlined.

Protect myself with a powerful enough backup system? What's wrong with ChronoSync and an external FireWire?

I see the risk of RAID0 if you aren't backed up, but with so many firewire options and backup software like ChronoSync and SuperDuper, I don't see any extra risk of data loss... aside from a drive failing and the time it takes to drive to BestBuy to replace it, then copy the stuff back from the external. I lost what, an hour?

If I'm missing something, please let me know.
 
We were talking about the risk/rewards of the various RAID levels. If you introduce a backup scheme, then that sort of changes the logic. Now we can talk about the speed advantage of RAID 0 and a backup, versus RAID 1 or RAID 5. Sounds like you have a good system and a good strategy. But you have to admit that there are a lot of people out there with no backup strategy at all!
 
RAID 0 for speed. Unfortunately they have no redundancy so if 1 drive fails you lose all the data.

RAID 1 for redundancy. Unfortunately a RAID 1 doesn't offer any speed benefits.

RAID 0+1 for increased speed (not as fast as a RAID 0) along with redundancy.

RAID 10 (1+0) is better than a RAID 0+1. It might be able to handle more than 1 hard drive failing, and is easier to rebuild than a RAID 0+1.

RAID 5 is better any of those, but OS X doesn't suppport it. You'l have to buy a RAID card or an external RAID tower that can do it.

I'm not really familiar with RAID 3, 6, etc...

EDIT: But yes on top of any of these solutions I would recommend a backup on an External Hard Drive, Blu-Ray Disc, Rev Drive, etc.
 
Sean Dempsey said:
I don't understand your logic here.

If I set up a RAID0, and have my data backed up to an external drive every night, I really don't see the risk. If I lose a drive, I just replace it and restore the data. And if I didn't have a RAID0... if I lose a drive, I just replace it and restore the data.

Everyone talks about how "if you lose a drive, you lose it all!!!"... what does that matter if it's backed up daily? Especially considering I'm using the same physical drive, it's going to fail in a RAID0, or it's going to fail on it's own. Having 2 drives in 1 array doubles my probability, but that's different than chances. I've had drives go 5 years strong and still haven't failed, lost after they were backlined.

Protect myself with a powerful enough backup system? What's wrong with ChronoSync and an external FireWire?

I see the risk of RAID0 if you aren't backed up, but with so many firewire options and backup software like ChronoSync and SuperDuper, I don't see any extra risk of data loss... aside from a drive failing and the time it takes to drive to BestBuy to replace it, then copy the stuff back from the external. I lost what, an hour?

If I'm missing something, please let me know.
Click to expand...

well you are right, but from what i have read/been told, you are most likely to lose a drive WHILE backing up, so if one of ur copies fail, and you buy a new drive and then back up to it, you are for the time while backing up, "technicly" at a higher risk of loosing your data if you only have one copy while backing it up to another.

Now..chances are..it wont happen that you loose two drives at the same time/day. BUT if it did and you lost your info well..you could have lost a lot or time/money/both.

From what I have read..you should have 3 copies of your data.

Brad
 
iBeard said:
RAID 0 for speed. Unfortunately they have no redundancy so if 1 drive fails you lose all the data.

RAID 1 for redundancy. Unfortunately a RAID 1 doesn't offer any speed benefits.

RAID 0+1 for increased speed (not as fast as a RAID 0) along with redundancy.

RAID 10 (1+0) is better than a RAID 0+1. It might be able to handle more than 1 hard drive failing, and is easier to rebuild than a RAID 0+1.

RAID 5 is better any of those, but OS X doesn't suppport it. You'l have to buy a RAID card or an external RAID tower that can do it.

I'm not really familiar with RAID 3, 6, etc...

EDIT: But yes on top of any of these solutions I would recommend a backup on an External Hard Drive, Blu-Ray Disc, Rev Drive, etc.
Click to expand...

Your post sounds suspect to me. It seems to me that the RAID 0+1 would be equal in speed to a RAID 0, just with half the space.

From the wikipedia article (and from what I 'knew' before), 0+1 is the same as far as redundancy and speed as 1+0 (RAID 10).

Raid 5 and 6 are similar, but 6 has two parity bits per row instead of 1. Also, RAID 6, upon single drive failure, can still function it also means that if 2 drives in the RAID set die, the data is still recoverable. RAID 3 and 4 are like RAID 5 only instead of distributed parity, they have a drive dedicated to nothing but parity. This makes it possible for HUGE performance issues upon drive failure, whereas a RAID 5 could be usable, at a speed loss, for a while.

And btw, RAID 5 isn't 'better' than anything, it's just a good option for some people. It's slower to write and has less space than RAID 0, and much less redundancy than RAID-1. It's an option for some but not for others; hardly 'better'.

EDIT: http://en.wikipedia.org/wiki/RAID

Someone also said my Dad's 4 disk RAID is 'living on the edge'.. well if 1% of hard drives fail, I guess we're up to 4%, right? I'll live.

I actually wish I could do RAID 5 for him, but the controllers are expensive.
 
Spikeanator6982 said:
well you are right, but from what i have read/been told, you are most likely to lose a drive WHILE backing up, so if one of ur copies fail, and you buy a new drive and then back up to it, you are for the time while backing up, "technicly" at a higher risk of loosing your data if you only have one copy while backing it up to another.

Now..chances are..it wont happen that you loose two drives at the same time/day. BUT if it did and you lost your info well..you could have lost a lot or time/money/both.

From what I have read..you should have 3 copies of your data.

Brad
Click to expand...



Well yeah, you gotta have your backup, and then a safety-backup. I have my active files in the raid, then all of them backed up every day to a external firewire, and then also backed up to an external USB (slow, but I don't leave it connected). So, at most, I'd be down 1 days worth of files, which for me isnt much.

But, I am going to order another FW800 drive for weekly disconnected backups, that way, if the raid and the external BOTH fail somehow, I am out a weeks worth of files, which is still pretty good.

But, as long as I know I have recent back ups externally located, I am totally comfortable risking it on the raid.

And if ALL of them fail, well, that's fate telling me something.
 
iBeard said:
RAID 1 for redundancy. Unfortunately a RAID 1 doesn't offer any speed benefits.
Click to expand...

I can't speak about the MacOS software implementation, but actually a properly designed software/hardware RAID 1 implementation DOES offer speed benefits in certain circumstances.

Whenever you have a disk write in RAID 1, you have to write to both drives. This will typically take longer than a single drive because the drive arm that holds the read/write head has to move to the proper place on the disk for *both* drives, and the disk write isn't complete until the *last* drive does its write.

Conversely, however, during a disk read, you only need to read from one of the two disks in your mirror. The controller send the read request to both disks, and so whenever the *first* drive of the two completes its read, you complete the disk read (and the controller can cancel or disregard the read from the second disk).

So, in a RAID 1 configuration, if your transactions are predominantly *writes*, you will be slower than a single disk. If your transactions are predominantly *reads*, you will be faster than a single disk. If you read/write in balance, only then is the performance essentially the same as a single disk. I should note that this applies during typical random disk access (common during most computer use). If you do few transactions that are large and sequential (might be the case if you use the system for video editing and aren't multi-tasking), different rules apply.
 
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