External Drive for Backups or Files

dmetzcher

dmetzcher

Metzcher.com
I just purchased a 4TB (2x2TB) external drive from OWC. I have two scenarios for its use and I'd like opinions on which is better. I have a lot of movies and video files (as well as other files that eat a lot of disk space).

My setup is as follows...
  • Mac Pro (late 2007 model)
  • 1x500GB internal drive (Main Volume, aka "Macintosh HD")
  • 2x500GB internal drives (RAID 0 - Used for Time Machine backup volume)
  • External enclosure with 2x2TB drives (eSATA output)

Scenario 1: Use the external drive as a secondary storage device.
In this scenario, I would keep the existing setup with the internal drives, and have a total of 500GB of space available for internal storage.
The external enclosure would have it's 2TB drives RAIDed together (RAID 1) with mirroring so that any video/miscellaneous files copied to it were copied to both drives (auto-backup). This means that I would have a total of 2TB of writeable space, instead of the full 4TB (2TB from each drive).

Scenario 2: RAID all internal drives together (RAID 0) and use external enclosure for Time Machine.
In this scenario, I would RAID the 3x500GB internal drives together (RAID 0) and combine them into one 1.5TB volume for Mac OS X. This would allow me to store all my files on the OS X volume.
I would also RAID the two external drives (RAID 0) in the enclosure (2x2TB) into one 4TB volume for Time Machine backups.

I'm leaning toward Scenario 2 because it's my understanding that RAIDing the three internal drives into a single volume will increase overall performance in terms of file save/copy operations. BUT...Will it decrease seek time when I'm accessing files?
EDIT: I spoke with someone at OWC and he stated that performance (read and write) on the internal drives will decrease slightly with this scenario. He did say, however, that it wouldn't be noticeable. Is this true?

I like Scenario 2 because it lets me keep everything on the same volume. I also like it because it allows me to upgrade the drives later to 1TB each and seems to provide the most flexibility. And, if there's ever a fire, I can grab the external enclosure in a hurry and run out of my house with my cats and car keys. :)

I'm really looking to get this right the first time, so opinions are what I need. Are there any performance drawbacks if I use Scenario 2?

Also, I've read that RAID will only work if the drives being combined are exactly the same (same size AND model number, etc). Is that true? I don't think OS X cares about this, but I've seen it as a warning on a lot of external drive enclosures that come with their own RAID controllers. Maybe it's just a CYA warning for those companies.

Thanks! Any help is very much appreciated.
 
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Ok, something about RAID.

1. RAID-1 is not backup.
2. RAID-1 is not backup.

But about your scenario 2. Raid-0 is fast both on read and write. On your case file access might be three times better. It is better to have exactly same disks. If not, the size and speed is measured by the slowest, smallest one.

If you do not need the speed, have you considered JBOD?
 
artov: Thanks for the reply... additional comments are below, but...

Are you saying that Scenario 2 seems like the better option?

artov said:
Ok, something about RAID.

1. RAID-1 is not backup.
2. RAID-1 is not backup.
Click to expand...

RAID 1 is mirroring, which is essentially a backup, no? Data is written to both disks at the same time, creating two copies of everything written.
http://en.wikipedia.org/wiki/RAID_1#RAID_1

artov said:
But about your scenario 2. Raid-0 is fast both on read and write. On your case file access might be three times better. It is better to have exactly same disks. If not, the size and speed is measured by the slowest, smallest one.
Click to expand...

All three internal drives are the same size. They are 500GB each.
Two were manufactured by Maxtor and are the same model.
The third drive was manufactured by Western Digital.
In terms of "exactly the same"... does that work, or do you mean the same manufacturer, specs, size, etc.?
(Good point on the slowest drive being the fastest performance I'll get. I had read that before but hadn't thought about it until you mentioned it.)

artov said:
If you do not need the speed, have you considered JBOD?
Click to expand...

I'd like the speed, so I'm inclined to go with RAID 0. From what I've read, compared with JBOD, RAID 0 gives me better performance. If it's a matter of "what happens if one drive in the array fails?"... I'm not really worried since I can replace it and restore from a Time Machine backup on the external drive. Let me know if I'm missing anything here or if there's a reason to go with JBOD, but I'm not worried about disk failure (of the internal disks) since I have a running backup (external)...if there are other benefits to JBOD that I'm not considering, let me know.

Thanks!
 
2x500GB internal drives (RAID 0 - Used for Time Machine backup volume)
Click to expand...
I highly recommend against using this type of RAID setup for what is, essentially, your backup volume. You have just doubled your chance of catastrophic failure without ability to recover data with this setup.

I would rather see a setup where you have a RAID 0 as a boot drive (for speed), and either a RAID 1 or no RAID at all for your backup.

Putting the fate of your backup in a striped array with no parity is begging for catastrophic failure, in my humble opinion. If one disk bites the dust, ALL data is lost, with no hope of recovery (sans sending the drive off for extremely expensive professional data recovery, and even then, good luck trying to rebuild and reassimilate that data into a RAID 0 setup).
 
ElDiabloConCaca: I hear what you're saying... but in order for such a failure to be of any concern, both my main volume and my backup volume would have to fail at the same time, correct? (What I mean is, a drive from my startup volume's array and a drive from my backup volume's array, would have to fail at the same time.)

I just want to confirm that that's what you mean, and not that my data on the two RAID 0 drives (that together make up the backup volume) is generally unsafe in terms of corruption due to general RAID 0 issues. Drive failure, yes, but are you saying that I could be writing data to these drives with no indication that one of the drives is not getting everything written to it (which would then cause me to not be able to restore from them)?

Just want to make sure I understand.

Unfortunately, since time machine requires twice the space in order to make the first backup, and since a single 4GB drive is expensive (are they even selling them yet?), it's very cost prohibitive to create a backup volume that is 2x2TB with only one drive. That's the issue I had.
 
True, you won't lose ALL data -- just the data on the striped drives.

I operate under the impression that a backup solution should be stable, reliable, and fail-safe (or at least as much as possible). With a striped array, non-statistically speaking, you have double the chance of data loss. Imagine if your main hard drive went kaput, and as you were restoring from the backup drive, a single RAID member went kaput as well -- you now have no data, with little chance of recovery.

I understand about the space concern, though. With a single 500GB boot drive, you should be able to fly with a single 500GB backup drive -- and having two 500GB backup drives in a RAID 1 would be more "fail-safe" than a 1TB RAID 0, even though you can "go back in time" farther with the latter.
 
ElDiabloConCaca: You've made me think about this a bit more and I think I have a solution that will work.

How about this...
I go with Scenario 2, as is, but I add another 2TB external drive (single drive, no RAID) and use this one to clone the OS X startup volume, say, every week or two. This was my old backup routine prior to Time Machine's arrival on the scene. I'd use SuperDuper and do it once a week.

This way, I'd have the RAIDed startup volume (speed), the RAIDed Time Machine volume (convenience), and the clone drive (piece of mind). I figure that if I lost a week's worth of files, I can live with that. Plus, I'd always have a clone of my drive, which is something I actually miss having. (Why even use Time Machine? Because I like the idea that I can quickly restore a file after accidentally deleting it or roll back a file to a month-old version.)

What do you think?
Some will call it overkill. I tend to be ok with overkill.
 
Sounds like good logic to me!

A nice, bootable clone never hurts in a complex computer setup -- especially with the potential amount of data (500GB) on your boot drive.

Ain't nothing wrong with overkill.
 
Here's a fun monkey wrench that was thrown into the works today...

I spoke with an Apple Genius a few hours ago. He told me that RAIDing three drives together (RAID 0) would be a problem because once you raid the first two, you are essentially raiding the resulting volume with the third drive. This will mean unreliability and a performance hit, he said.

Is this true? I thought that using RAID 0 and striping three drives together wouldn't be any different than RAIDing two. He did mention concatenated RAID, which is JBOD, which is NOT RAID 0 (it's technically not even RAID at all). I'm confused now. Is he right? Is there a problem in general with striping three drives as opposed to striping two?

The solution, as I see it, is to just replace all the internal drives with two 1TB drives and RAID them together into a 2TB volume, if what he says is true.
 
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To create a RAID with 3 volumes, you would stripe all three drives at the same time... It sounds like the genius you spoke with thought you wanted to stripe two, then add a third to the RAID (which you cannot do).

There is no difference in procedure for striping two vs. three drives.

Of course, making a RAID is the same as formatting a drive, so you lose all data... Which means if you're going to stripe a drive with data on it and want to retain the data, you'll need to find somewhere to back it up first.
 
OK, great. Just wanted to make sure before I started.

ElDiabloConCaca said:
Of course, making a RAID is the same as formatting a drive, so you lose all data... Which means if you're going to stripe a drive with data on it and want to retain the data, you'll need to find somewhere to back it up first.
Click to expand...

Yup... I'm going to use the external drive (one of the drives in the enclosure) to clone the disk. Then I'll boot from it and RAID the three internal drives into a single volume and do another clone back onto the new combined volume.

That's the plan, anyway... crossing fingers and buying an external, 2TB "cloning" drive today for piece of mind. :)
I won't start Time Machine backups on the new volume until I have the cloning drive so I'll have a good copy of the original clone to roll back if anything goes wrong.

Thanks for all your help, ElDiabloConCaca!
 
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One, final recommendation (which is more opinion than fact):

Stay away from Seagate drives. Go Western Digital if at all possible.
 
I'm done... and here's what I'm noticing.
(To recap, I've used RAID 0 -- striping -- to combine three 500GB hard drives into a single startup volume called "Macintosh HD".)

First, holding option key during startup provides me with three options:
Macintosh HD 1
Macintosh HD 2
Macintosh HD 3

Selecting ANY of them gives me a gray screen, no Apple logo, and then, eventually, a circle with a line through it (logo). It will not boot past that logo.

I can boot if I boot into my backup drive, open System Preferences, and choose my boot volume (Macintosh HD -- just one of them, not three like the startup screen shows... clearly OS X understands this is just one volume once the OS is up and running).

Why is this? I'm about to do a restart and hope that it just needed to boot into the drive once to understand that it's just one volume the next time it boots, but I'm not too hopeful... if that's the case, I'll be shocked, actually... it's terrible design on Apple's part given that the system should know that it's a single volume as it created the volume for me.

==========================

Second, performance seems slow. Like, really slow. It took at least 8 minutes to go from the login screen to a desktop with icons, menu bar, and dock. Even then, I had to kill a few things that hung during startup (QuickSilver and something else). I launched Photoshop...5 minutes (when it used to be ready to use in less than 20 seconds). I launched Safari...it took about a minute (I consider that VERY slow). Spotlight is indexing the drive(s) right now, so maybe that's causing the performance hit, but I don't know. It's been a while since I've had to wait for Spotlight to index a drive, and there's 500GB of data to index. I just launched Firefox and it came to life in less than 30 seconds. Maybe performance is increasing now. Maybe something was going on because it was the first time I booted into this new volume?

Is there some suggested benchmarking software that I can run (preferably free, since I've already sunk enough money into this little upgrade) and compare it against some average results?

Any help that can be provided will be greatly appreciated. I'm about ready to scrap the three internal drives and buy a single 2TB drive. I want to avoid that and save a little cash, but if this is the performance I can expect, it just won't do. :(
 
I restarted. Five minutes to boot to desktop and launch my startup items. I think that's a few minutes longer than it used to be when I was using one single 500GB drive for startup. Spotlight is still running, of course... and I forget how much of a performance hit Spotlight adds, so maybe someone else can tell me "It's Spotlight, no worries."

A piece of good news... when I restarted and held the Option key, I was able to select one of the "Macintosh HD" drives (there are three listed) and use it to boot. It's still ugly that there are three drives there. Is there a way to tell OS X to "stop being foolish... it's just one volume"? I wonder what will happen if I select another of the drives next time. I'll test that. I've searched the web for an answer to this, but found nothing.

Once Spotlight is done, I'm going to restart again. Who knows when that will be. It's getting late.

(I'm going to keep posting about all this as time goes on so that others may benefit from knowing what happened along the way. Maybe, if it all goes downhill for me, someone else can be spared.)

Any help or advice that can be provided, as always, will be appreciated. :)
 
Well... no change. The 3x500GB startup volume is just really slow. Here are the differences between it and a 2TB drive that I've got installed right now.

3x500GB (RAID-0) Volume...
Boot to login screen: ~5 minutes
Login screen to desktop: ~7 minutes
Spinning Beachballs... yeah, I've got lots of them.
Launch Photoshop: several minutes

1x2TB Volume...
Boot to login screen: ~1 minute
Login screen to desktop: ~30 seconds
Spinning Beachballs... nope... it's very snappy.
Launch Photoshop: ~30 seconds

I'm thinking, at this point, that grabbing a single 2TB drive and using it for my startup volume is what I should do now. The one I'm using for this testing is a backup drive that's part of an external 2x2TB RAID enclosure, so I need to put it back into the enclosure and can only use it temporarily. Maybe I can get a nice 10,000 RPM drive for added speed.
 
I've got a friend urging me to get a hardware RAID card instead of replacing the three internal drives with one large one. Any thoughts?
 
Cost of a hardward RAID controller for Mac Pro (from OWC): $680 + $80 cable.
No thanks, on that one.
Looks like a 2TB internal drive is the only option left. I'm going to try and find one with a 64MB cache (Western Digital has one) and 7200RPM (no "green" drives).
 
Strange -- I wrote an entire post on the difference between "fake RAID" (Apple's implementation) and "real RAID" (hardware implementation), and now I can't find it anywhere in this thread.

Maybe I am going nuts today...
 
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