Striping and Partitioning
 

I have a G5 Tower and am trying to RAID (0) a pair of external Firewire Drives using Apple Disk Utility. The only problem is that Disk Utility doesn't seem to partition RAIDed drives. Which is incredibly lame, considering that today's disks are huge, and a 400gb array is kind of useless for anything other than video work. Anyway, is there any way to trick Disk Utility into partitioning the drive? Do I have to buy SoftRAID or another 3rd Party striping utility? Will a third party disk utility do it safely once I've striped the drive using apple's disk utility? Help! Thanks.

So why are you RAIDing two firewire drives if you're not interested in doubling the capacity? If you want two drives, then don't RAID them!

Speed, my friend, speed.

Then go get a hardware raid card and mount the drives inside the case. Striping for speed then using software to handle the data seems counterproductive.

Did you partition first, then create the raid set, or the other way?
Are you using 2 different firewire ports?

My question is; How are two 200GB partitions more useful than one 400GB drive? Since in either case they would be split between the same RAIDed drives. If one fails they both fail. I find it much more convenient to have one very large drive organized sensibly than multiple smaller drives running down the side of my desktop.

2 x 200 striped will have much better performance than 1 x 400 as you have data coming off 2 heads at the same time
IF the rest of your system is fast enough to keep up with the drives. Any bottleneck like a slow interface card or software raid makes it all a somewhat academic exercise.

The data integrity is really a wash - one 400Gig drive going south isn't any different than a 2 x 200 raid set waving it's legs in the air.

Now, if you add a third drive, and stripe with parity you can have it both ways :D

This still doesn't answer my question. How is 2x200GB partitions of a RAID better/faster/more-convenient that 1x400GB RAID (Both created from the same 200GB pair of drives)?

Aahhhh - I see.

none, except for the usual advantages of partitioning.

I will probably end up buying a card eventually, but this is my el cheapo option in the meantime. (I'd have to buy two SATA enclosures plus the card so I can use the two internal drives I've already got, plus then I'd lose the speed and reliability edge from the SATAs by having them running over firewire, whereas I already have the two external ATAs, so why not try to squeeze the maximum performance out of them?) My internals are fast, and I have the externals already. Having already tried striping them with the apple software raid I can attest that they are damn fast -- noticably faster than my internals. I don't need 'fastest,' just fast. However the striped array is too big. I am using this for scratch disk space and occasional audio editing. For maximum speed and stability, I would prefer one or two smaller clean volumes at the center of the disk -- say a 30-or-40-gig partition. And then I can just use the rest of the disk for general storage.

But anyway, does anybody know the answer to my question? Do I have to buy SoftRAID or something?

Vegas - Smaller volumes have faster seek times because there's less disk to seek thru. Partitions at the center of the disk (adjacent to the spindle) read and write faster than data stored futher out on the physical platen because of latency and head seek issues -- there's less space for the head to move over, and you don't have to wait as long for interleaved data to come around again. A clean volume is advantageous because it's not fragmented. So that's my ideal for a scratch disk.

Do I have this right? The goal of the original post is to take two drives, put them together as one (RAID) and then partition the RAID into two or more drives. Why doesn't this make sense to me? If you really want to partition, why not partition one or both of the two drives and not RAID them?

As previous posts mentioned, the speed you're after isn't going to be there with a software RAID. Even with hardware, I doubt you'd notice. Failure is another consideration. When a RAID fails, it usually fails completely.

Why no speed increase?
 

A. I can tell that my drives are faster, even just with software raiding

but,

B. Why wouldn't you see a speed increase, especially with a hardware controller? A hardware-based array of 2 drives should give you at least 1.8x the speed of a single drive, until you max out the bus. You'll keep losing speed as command/disconnect overhead increases; obviously hardware will be faster than software.

C. When a striped set fails, it fails completely. When any other raid configuration fails, it's safer than a single disk. That's the whole point.

Try this:

http://www.barefeats.com/fire33.html

Hi leoYWCA,

As Rob-art pointed out in the page you linked to above, putting both drives of a FireWire RAID on the same FW400 channel will not get you any significant additional speed. Look at the "Dual FW, One Channel" bar in the graphs at the linked page.

Now, if you are using two FW800 drives, you may get some advantage. But not with two FW400 drives on the same FW channel.

As for your question, can you stripe and partition with Apple's built-in software RAID? If you can't get it to do that easily, then I doubt it can be done at all. (Although I will readily admit I've never tried, so I couldn't say for sure.) What I think many of the people in this thread are trying to communicate to you is that whether or not you CAN do it, there's not a whole lot of advantage to doing it.

You also seem to have some misconceptions.

When you partition a drive, whether it is a single drive or a RAID set, the head is forced to access BOTH partitions, bouncing back and forth between the first and second partition as required. This slows down access, it does not speed it up.

On the other hand, it is true that read/write to areas at the center of the platter is faster than to areas at the outer rim. But partitioning the center vs. the outer rim and using the outer rim will slow down overall access. If you really want this speed advantage, you will need to dismount the partition at the outer rim, so that the head does not have to bounce back there continuously.

Also, the discussion above has all been assuming a single platter. Most desktop drives nowadays have multiple platters and heads, which complicate the picture to the point where these "rules" make far less impact, or at least they are less easy to work out how to gain benefit exactly.

Trevor

Exactly. Plus, any benefit you gain from doing it won't be as great or as noticeable as if you spent the money on adding RAM, a new video card, or even a new, faster system.

Thanks Trevor, et al.

I did not realize that the drive would "bounce" thru both partitions. However, I don't mind dismounting the extra partion to avoid that. (I would have thought that if the directory is accurate [which it better be!], it would keep the drive seeking in the partition that is designated in Photoshop, etc., but I guess this is not the case.) I am planning to use an additional controller, so I can take advantage of the speed gains noted in that benchmark. I would also think think that partitioning a raided volume would result in matched physical locations on the various drives, (as long as they are matched drives, which mine are) otherwise I asume you take a huge hit in speed, right?

As for buying a new system, etc., I can't afford it, and frankly my system is pretty good. Like I said, I just want faster, not fastest. And the slowest element of my system, as with most, is drive I/O. I think that you are right that the apple software won't do it, and I am looking to buy softRAID now. I don't think that I have a cost effective alternative. But I have a very specific application for my array -- scratch disk space. And so having a giant volume will sort of ruin the whole thing unless I just let the extra 150-gigs go to waste. As soon as I start putting other things on there the drive will get fragmented and there goes the show. I could scrap the RAID thing and just buy a really fast drive, but that is also kinda pricey. Must do more research....

What are you using it for and how much RAM do you have? The reason adding RAM often speeds up a system is because it reduces disk access. That might be the cheapest and best solution.

Photoshop (mostly) scratch disk. I have 1.2 gigs of RAM. I'm sure more RAM would help, but given the size of the files I often work on, there's really nothing that's going to substitute for faster disk access.

ps - I really appreciate the help, guys. thank you.

Photoshop loves RAM! I would be shocked if doubling your RAM didn't make a big difference in speed, especially if your files are large. Increasing RAM will reduce the need for scratch disk space, and RAM is the cheapest upgrade you can do.

The only problem is that Photoshop only supports up to 2 gigs of RAM. I already have 1.2 gigs. So while I'm sure that I can pull out some extra performace that way, it's only going to go so far, I think.

Ok...here's the deal with Photoshop. It does in fact love to eat up Ram. And it does in fact have a 2Gig limit...however... if you have 1.2 gigs of available Ram, and Photoshop is running as well as the OS and other smaller apps (maybe mail, or whatever else may be running in the background), then Photoshop is really only using about a Gig of that Ram. Photoshop cannot and will not use all the Ram available on any machine because then the OS would'nt be able to run in conjunction with Photoshop. So, in this case, 2 Gigs of Ram would mean that Photoshop would likely use about 1.8 or so of it, and leave the rest for the OS and other functions. My G5 has 1.25 Gigs of Ram and Photoshop seems to really fly, however, at work, my G5 with 2 Gigs beats the snot out of my home based mac...and the Ram allocation is the only difference between the two. Ram is always the best option to upgrade first when doing any kind of photo or video editing. Ram will always be faster than any Harddrive. Take a look at Ramseeker.com. There you can find some really great deals on Ram for your G5.

VegasMac...
-Out

VegasMac is absolutely right. Check your Phoshop preferences: Memory & Image Cache settings. The Maximum Used by Photoshop is probably set at 67 %. Quit other applications and increase that to 80%, then restart Photoshop. See if that relatively small increase in RAM used doesn't make it faster. Notice too that the available RAM is much less than 1.2 gigs.

While all applications will benefit, few will see as big of a performance jump with increased RAM as Photoshop. Buy more RAM!!! You won't regret it.

"Buy more RAM!!!" -- haha! ok - I will!
I also went ahead and picked up softRAID -- it just seemed like a good thing to have. I am going to experiment with partitioned and non-partitioned scratch disks over firewire and I'll post the results once I get around to doing this.

Let us know how the extra RAM does too.