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all2ofme · Oct 28, 2006, 03:44 PM

Hi all,

I've just put two WD5000YS drives (500GB each) into my Mac Pro and am setting them up in RAID 0 so that my Photoshop/Aperture work will hurtle along yet further.

I've read all manner of things on RAID but am still confused as to what block size I should be using for them. All of my files are well over the 256KB max listed in Disk Utility (they'll be 4MB up to several hundred MB), but I'm assuming there's more to it than that...

Does anyone have a good rule of thumb to use for this?

Thanks in advance.
Ben

mac128k-1984 · Oct 28, 2006, 03:46 PM

My rule of thumb for the raid 0 blocksize - use the default. Works well enough for me and I've noticed a large increase in speed.

all2ofme · Oct 29, 2006, 07:57 AM

Thanks for the reply - I've gone for the default (32k) and will see how it works out.

Will be interesting if anyone chimes in with some reasoning behind going for a value near either end of the possible choices.

mac128k-1984 · Oct 29, 2006, 08:52 AM

From what I've read over in the apple discussion forum the majority of people there use the default also

all2ofme · Oct 30, 2006, 08:04 PM

Hi mac128k - I'm copying 215GB from one RAID 0 partition to another (both RAID partitions being spread across the same two drives) and the dialog box is suggesting that it'll take about 3 hours. That sounds slow, doesn't it?

The Disk Activity tab in Activity Monitor is showing 31.71MB/sec. Which also sounds slow, don't you think?

CatOne · Oct 30, 2006, 09:03 PM

Er... WHY do you have two separate RAID 0 partitions set up on the same physical drives? I would EXPECT terrible performance... you are chewing those poor drives to pieces, because you're making the heads constantly try to be in two places at one time.

Of course the activity monitor shows things as slow. Seriously, you just partitioned each drive in two and created 2 RAID 0 sets? LOL! That's way worse than just leaving them as 2 separate drives. Way less safe, and slower to boot!

all2ofme · Oct 31, 2006, 03:44 AM

Ha! When you put it like that it starts to make sense

Is there a way to end up with the RAID set as two separate partitions? My rationale was that there'll be a good portion of expendable data across the stripe and I could keep that elsewhere so as to make a back-up of the rest simpler.

mac128k-1984 · Oct 31, 2006, 07:53 AM

Why not setup a Raid 0+1 setup, that is mirror your stripped disks. You'll get some of the speed improvements of raid 0 but the safety of raid 1.

Another alternative is do what I do. I have a raid 0 setup and at night I backup it up to another drive. This gives me all of the performance of a raid 0 and no raid 1 performance penalty.

I go by the KISS mentality and keep things simple. To be honest I think your either over analyzing things or you're building a complex setup that may give you more headaches in the long run. While hard drive failure is bad, no question, it is rare. If you have a good backup strategy you can mitigate the effects of losing your data - at least that's how I see things.

all2ofme · Oct 31, 2006, 09:21 AM

I don't want to fill my machine up completely with disks (for money and noise reasons) so a RAID 1+0 (or the reverse) isn't an option I want to explore. Nor would these give me the safety net of a genuine back-up.

I like the KISS mentality too - what I was trying to do was make myself a partition that I could fill with things that I could afford to lose (i.e. not back up). Things like mp3s and DVDs.

The other partition was to be for Aperture/Photoshop files and general storage. Not needing to go beyond 500GB for that I figured it'd be a good idea to save the money that'd be needed to back up a full TB and get myself a 500GB FW800 drive to use. Perhaps I should just be putting everything on a 1TB back-up drive. Unless there's a better way to divide up the data (or my back-up plan).

all2ofme · Oct 31, 2006, 07:53 PM

About to blat the lot as a single 1TB RAID 0 partition unless anyone has any last minute advice.

Hopefully this is the right thing to do

all2ofme · Nov 2, 2006, 12:15 PM

When duplicating a folder on the new 1TB RAID partition I get about 40MB/second. Does that sound about right? I'd thought a duplicate would be faster than that, though perhaps I've lots more to learn...

all2ofme · Nov 4, 2006, 06:44 AM

I may well be talking to myself (

), but I'm suspicious that even having the two drives striped as one partition isn't giving me much of a speed increase.

Does anyone know of a decent free disk benchmarking tool. I've had a google and a search here but not turned up anything so far.

Thanks for any help.

Tsilou B. · Nov 4, 2006, 09:34 AM

Originally Posted by all2ofme

When duplicating a folder on the new 1TB RAID partition I get about 40MB/second. Does that sound about right? I'd thought a duplicate would be faster than that, though perhaps I've lots more to learn...

Yes, that sounds absolutely right. If you copy files from one RAID system to another one and get only 40MB/s, that would be horrible performance, but as long as you're reading from and writing to the same RAID partition, 40MB is really ok.

I may well be talking to myself ( ), but I'm suspicious that even having the two drives striped as one partition isn't giving me much of a speed increase.

It does give you much of a speed increase (almost 2x), but only the transfer rate is increased. The seek time is not decreased. If you duplicate a file, the drive has to seek all the time, because it jumps between the position where the original is saved and the destination block. And because this part is not accelerated, the duplication is not that much faster than a single disk.

When you copy a file from one RAID to another one, or you simply read a file from the RAID into memory, you do get the expected performance increase.

chris v · Nov 4, 2006, 12:08 PM

Originally Posted by all2ofme

When duplicating a folder on the new 1TB RAID partition I get about 40MB/second. Does that sound about right? I'd thought a duplicate would be faster than that, though perhaps I've lots more to learn...

You're still reading & writing to the same RAID drive simultaneously. Of course that'll slow things down.

all2ofme · Nov 5, 2006, 05:11 AM

Thanks for the replies - it does all make sense. What confused me was that the performance was better this way than it was with the two partitions (40MB/second instead of 31MB/second). Having seen some sort of improvement I'd assumed I'd get more than I did.

I've just tried copying from my stock drive to the array and get just under 70MB/second, so that's more like it. Hooray!

Now that it's all set up properly I'll get some real work done

Drizzt · Nov 5, 2006, 05:06 PM

Originally Posted by mac128k-1984

Why not setup a Raid 0+1 setup, that is mirror your stripped disks. You'll get some of the speed improvements of raid 0 but the safety of raid 1.

Another alternative is do what I do. I have a raid 0 setup and at night I backup it up to another drive. This gives me all of the performance of a raid 0 and no raid 1 performance penalty.

I go by the KISS mentality and keep things simple. To be honest I think your either over analyzing things or you're building a complex setup that may give you more headaches in the long run. While hard drive failure is bad, no question, it is rare. If you have a good backup strategy you can mitigate the effects of losing your data - at least that's how I see things.

Instead of going with Raid 0+1 and losing 50% of the available disk storage capacity, I'd go with Raid-5 and lose N-1 drive while still having the performance gain and security. (Assuming it's available on the MacPro)

all2ofme · Nov 5, 2006, 07:03 PM

Yeah, I thought that too (though it wouldn't be as fast as the RAID 0). It's not available on the Mac Pro without a separate RAID card, sadly. Unless you want to run OS X Server - I think that supports RAID 5 in software.

RAID 0 and a good back-up has me happy for now, though. I was using Photoshop this afternoon and it flew.