[voodoo]

The XServe uses IDE HDs, yet once SCSI HDs were considered better HDs for servers. Has this changed?

Are IDE HDs as fast as SCSI?
Do IDE HDs rely alot on the CPU compared to SCSI?
Are IDEs mass manufactured, but SCSI HDs made with care (Hyundai vs. Bentley)
What about data throughput?

I mean back in the day there was a lot of difference between those types of HDs. Have those differences been solved? Could one say Apple made the right decision to put IDEs in the XServe instead of SCSIs?

[CatOne]

Originally posted by voodoo:
The XServe uses IDE HDs, yet once SCSI HDs were considered better HDs for servers. Has this changed?

Are IDE HDs as fast as SCSI?
Do IDE HDs rely alot on the CPU compared to SCSI?
Are IDEs mass manufactured, but SCSI HDs made with care (Hyundai vs. Bentley)
What about data throughput?

I mean back in the day there was a lot of difference between those types of HDs. Have those differences been solved? Could one say Apple made the right decision to put IDEs in the XServe instead of SCSIs?

Ah, a nice question

IDE HDs are not as fast as SCSI drives where disk rotation is concerned. Parallel ATA drives are I believe around 7200 max, and SATA drives (Serial ATA) are up around 10,000 max. Currently the fastest SCSI drives are 15,000 RPM drives, which means the seek time will be faster on them.

But that's not the whole story. The *main* knock on IDE drives where speed is concerned is on bus contention -- with a parallel bus and a few drives hanging off them everything gets SLOW. The Xserve uses 4 independent IDE channels, each with its own controller, so this issue pretty much goes away. If you set up a RAID 0 with all 4 drives in an Xserve it is FAST -- believe you me ;-) The Xserve gives up NOTHING to SCSI drives in throughput -- you can theoretically push 133 MBps times 4 channels which is 550 MBps... which is a higher theoretical limit than Ultra SCSI 320 (which is a shared bus).

As for reliability -- in general IDE drives don't go through the same QA treatment at the factory as do SCSI drives. This is why the SCSI drives are more expensive, and why they generally have a 3 or 5 year warranty versus IDE's 1 year (typical). In this case Apple individually tests and certifies each drive as "perfect" before it's shipped -- so you get the same reliabilty. The testing is actually more exhaustive than the SCSI drives go through at the factory.

As for throughput... well again it's architecture, and Apple's is a good one. If you want speed... check out an Xserve RAID. I ran 'iometer' from a PC against an Xserve RAID with a 14 disk SCSI 50 setup... I only got a throughput of 310 MEGABYTES/sec. Heh. We're talking 5000 64KB reads *per second*. And that's with ATA drives.

Fast enough for you?

[OreoCookie]

Originally posted by voodoo:
The XServe uses IDE HDs, yet once SCSI HDs were considered better HDs for servers. Has this changed?

Are IDE HDs as fast as SCSI?
Do IDE HDs rely alot on the CPU compared to SCSI?
Are IDEs mass manufactured, but SCSI HDs made with care (Hyundai vs. Bentley)
What about data throughput?

I mean back in the day there was a lot of difference between those types of HDs. Have those differences been solved? Could one say Apple made the right decision to put IDEs in the XServe instead of SCSIs?

Really depends what you are doing. SCSI drives' main advantages are: 1. faster seek time and 2. better reputation in terms of reliability. But also SCSI drives can fail (two drives in our AlphaStations failed last year).

For almost all stuff I can think of, SCSI is not worth the money. Highly complex CAD constructions or databases benefit greatly from smaller seek times.

But now, you get a lot more bang for the buck with ATA drives. (An exhaustive review of the well-known c't magazin comes to the same conclusion; they have replaced their old backup solution with a new ATA RAID backup station.)

[SMacTech]

IDE drives do require more CPU time then SCSI do. However, with Apple's implementation of a dedicated controller for each channel, this is less of a problem than previous.
SCSI is also asynchronous with data flowing in both directions at the same time, whereas IDE is not.
As for reliability, I have seen six 15k rpm Fujitsu 36gb drives give up the ghost in 18 months in our Dell <cough> PowerVault Raid. Thankfully Fujitsu has a no questions asked return policy.
I am sure Apple did the best thing for balance of speed, cost and reliability in their RAID implementation.

[dfiler]

I'm curious SMacTech, by 'require more CPU time', do you mean the CPUs of computers connected to this NAS over fibre channel? The same question goes for your comment about 'flowing in both directions at the same time'. Does this mean between the XServe and attached computers? I was under the impression that the XServe's hardware was abstracted, hidden behind the fibre channel and internal processing.

My company has been looking at storage devices for a while. The topic definately makes for fascinating reading and purchasing research. Normally, I don't knit-pick the details in posts, but these devices are aimed at markets where off-hand advice and anecdotes aren't typically sufficient.

[OreoCookie]

Originally posted by dfiler:
I'm curious SMacTech, by 'require more CPU time', do you mean the CPUs of computers connected to this NAS over fibre channel? The same question goes for your comment about 'flowing in both directions at the same time'. Does this mean between the XServe and attached computers? I was under the impression that the XServe's hardware was abstracted, hidden behind the fibre channel and internal processing.

My company has been looking at storage devices for a while. The topic definately makes for fascinating reading and purchasing research. Normally, I don't knit-pick the details in posts, but these devices are aimed at markets where off-hand advice and anecdotes aren't typically sufficient.

If you connect an XRaid to an XServe (or a PowerMac), it won't need any more CPU power than a SCSI drive. Even usual ATA drives don't consume noticably more CPU power. Reason: DMA (direct memory access) has been implemented for years now.

Even if there should be a difference, computers get increasingly faster, so the fraction you loose nowadays is really negligible.

What does your company want to do the RAID system anyway?

[jcadam]

Back in the day, SCSI used to be MUCH better than IDE. Nowadays, it ain't. The only reason IDE hard drives are running at 7200 rpm is so that drive manufacturers can make sure there is a performance differential between their IDE and SCSI offerings.

As the difference between SCSI and ATA narrows, I expect Serial ATA to replace SCSI.

[dfiler]

Oops. Just realized that we're discussing the XServe and not the XRaid. Please disregard my previous post.

I would tend to agree with the prevailing sentiment on the web; that the performance gap between IDE and SCSI is now _almost_ trivial. Software configuration can easily account for larger performance disparities.

In some instances, that difference will be critical. Yet, if someone really needs the fastest storage/disk-access available, Mac hardware is probably not best suited to the task anyway.

[OreoCookie]

Originally posted by dfiler:
Oops. Just realized that we're discussing the XServe and not the XRaid. Please disregard my previous post.

I would tend to agree with the prevailing sentiment on the web; that the performance gap between IDE and SCSI is now _almost_ trivial. Software configuration can easily account for larger performance disparities.

In some instances, that difference will be critical. Yet, if someone really needs the fastest storage/disk-access available, Mac hardware is probably not best suited to the task anyway.

ATA doesn't eat up CPU cycles anymore for the reasons I have given above.

And even if a fast storage system is needed, it might not make any difference at all. If there is just 100 MBit ethernet, ATA drives (one ATA drive) has sufficient power to saturate it. If you need it locally or you are connected via Gigabit ethernet, this might be another story.

Still, only a few applications benefit that much from SCSI that it would actually pay off.

[schalliol]

My Ultra2 SCSI array is SLOW (dual 7200RPM Seagates with 4MB Caches - 9GB each) compared to the IDE arrays under Apple's software.

SoftRAID should be out in not that long and might make a difference in this regard. I sure hope so. Otherwise I guess I might consider replacing the array with a second IDE array, this time on a RAID card. However, I don't have any money for that at the moment, so it will have to wait.

I wonder if that quad bus IDE RAID card is out yet.

[SMacTech]

Originally posted by OreoCookie:
Even usual ATA drives don't consume noticably more CPU power

I can easily notice the difference under taskmanager in Windows 2000 between IDE and SCSI cpu utilization. We have a 200gb IDE as a mirror drive that we robocopy to each night and another SCSI 73gb ultra3 drive. When writing to the IDE it jumps noticably. IDE is certainly catching up with SCSI, but I suspect Serial SCSI may change that yet again.

Although somewhat dated and IDE has improved greatly, this page outlines many of the differences between SCSI and IDE.

[OreoCookie]

Originally posted by SMacTech:
I can easily notice the difference under taskmanager in Windows 2000 between IDE and SCSI cpu utilization. We have a 200gb IDE as a mirror drive that we robocopy to each night and another SCSI 73gb ultra3 drive. When writing to the IDE it jumps noticably. IDE is certainly catching up with SCSI, but I suspect Serial SCSI may change that yet again.

Although somewhat dated and IDE has improved greatly, this page outlines many of the differences between SCSI and IDE.

Well, the point is, depending on what the machine does, the extra CPU utilization might not be noticed at all. Just think of another example: To saturate a 100 MBit ethernet link, one needs 30-40 % (depending on the driver) of a 400 MHz CPU running Linux. Now replace that 400 MHz CPU with a current 3 GHz P4. It can handle that single link on the fly.

Same with HDs.

BTW, your article has one serious flaw:

Here's another interesting note about native IDE/ATA support under NT: Currently, NT's highest supported ATA PIO mode is PIO Mode 2, which defines an 8.3MBps burst data transfer rate. Even if you use a Fast ATA-2 subsystem capable of 16.6MBps with a PIO Mode 4 drive, under NT you realize a maximum potential throughput of only 8.3MBps.

Windows is not stuck at PIO mode anymore (which means that the data has to be shoved through the CPU). All modern hds support DMA (direct memory access) that circumvents the CPU.

Additionally, if you have an XRaid or something similar, that extra won't make any difference: the XRaid hardware takes care of it.

[OreoCookie]

Originally posted by schalliol:
My Ultra2 SCSI array is SLOW (dual 7200RPM Seagates with 4MB Caches - 9GB each) compared to the IDE arrays under Apple's software.

SoftRAID should be out in not that long and might make a difference in this regard. I sure hope so. Otherwise I guess I might consider replacing the array with a second IDE array, this time on a RAID card. However, I don't have any money for that at the moment, so it will have to wait.

I wonder if that quad bus IDE RAID card is out yet.

Hardware RAID (ATA!) cards are slower than software RAIDs. At least for PCs this is the case. Unless you pay for SCSI again, but this doesn't make sense for most people.

[schalliol]

The real problem is the lack of software on the Mac that's any good. With the OS X SoftRAID coming out soon we should see some substantial improvements.

[SMacTech]

Originally posted by OreoCookie:
Well, the point is, depending on what the machine does, the extra CPU utilization might not be noticed at all.

BTW, your article has one serious flaw:

Here's another interesting note about native IDE/ATA support under NT: Currently, NT's highest supported ATA PIO mode is PIO Mode 2, which defines an 8.3MBps burst data transfer rate. Even if you use a Fast ATA-2 subsystem capable of 16.6MBps with a PIO Mode 4 drive, under NT you realize a maximum potential throughput of only 8.3MBps.

Windows is not stuck at PIO mode anymore (which means that the data has to be shoved through the CPU). All modern hds support DMA (direct memory access) that circumvents the CPU.
.

Yes, I had pointed out that the article was dated. I agree that current CPUs probably are not affected by the cpu hit that IDE has over SCSI.
My experience in the past 10 yrs has always proven SCSI to beat out IDE in performance, certainly at a much greater $ expense.
In October, I will be purchasing an XServe and I am getting anxious to replace those last few Windoze servers with it. I can then see how the IDE RAID performs for myself.

[nerd]

I just set up a RAID at work with the ATTO card and 2 IBM 10k RPM SCSI 3 drives that Otherword Computing is selling. When using ATTO Express stripe to bench test, the RAID got the same numbers as the internal IDE drive at the start of the test. Towards the end of the test the the IDE started to loose about 5 megs/sec which could easily be because there is already data on the boot drive unlike the new RAID.

We're upgrading a couple Media 100's at work. If I had my way I would have done IDE but Media 100 won't support IDE for the capture drives. They say there is some kind of bug in their drivers that doesn't like IDE. WTF.

Brad

[OreoCookie]

Originally posted by SMacTech:
Yes, I had pointed out that the article was dated. I agree that current CPUs probably are not affected by the cpu hit that IDE has over SCSI.
My experience in the past 10 yrs has always proven SCSI to beat out IDE in performance, certainly at a much greater $ expense.
In October, I will be purchasing an XServe and I am getting anxious to replace those last few Windoze servers with it. I can then see how the IDE RAID performs for myself.

A friend of mine works with XRaids. The performance for media type of stuff is excellent (video, etc.).

[ferg]

ok, so on the low end, I have a dual GHZ Quicksilver - no scsi, but have a few 9 gig drives from my old b&W G3(Seagate barracudas 7200RPM). Looking at the Adaptec 2906 card(10MB transfer) or the 2930U(20MB), is it worth it to get the faster card? I was just going to use them for storage space, but then I was wondering if it would be better to install the OS on one and run it off of the scsi drive with the faster card, but is it faster than the ATA100 80gig drive in there now??

And if I did add the drives, manage to figure out the termination properly(any help there would be cool, I am assuming as long as they are different #'s and the last drive on the chain is terminated i am OK), would the OS be happy on those drives?

Help!?!

Thanks!

[schalliol]

I have a dual GHZ Quicksilver - no scsi, but have a few 9 gig drives from my old b&W G3(Seagate barracudas 7200RPM). Looking at the Adaptec 2906 card(10MB transfer) or the 2930U(20MB), is it worth it to get the faster card?

Depends on the drives, if they're ultra SCSI as opposed to fast-SCSI, yes.

I was just going to use them for storage space, but then I was wondering if it would be better to install the OS on one and run it off of the scsi drive with the faster card, but is it faster than the ATA100 80gig drive in there now??

No, the ATA drive will pretty much surely be faster. If you had an older machine you could use 3 or 4 SCSI drives as a RAID 0 array and that would be pretty fast, but you'd need a better card/set of drives and it still might not be good. (new world machines can't boot off of SCSI RAID 0)

And if I did add the drives, manage to figure out the termination properly(any help there would be cool, I am assuming as long as they are different #'s and the last drive on the chain is terminated i am OK)

Basically so. People argue there are better terminators, etc. That is true, there are some really nice active terminators that should speed performance up, but in general: Yeah.

, would the OS be happy on those drives?

Should be happy on ONE of those drives or multiple drives formatted as RAID 1 (mirroring-redundancy). However, I'd go with the ATA for your boot and use a RAID 0 to create a faster multi-drive array for your storage if the drives are the same. Keep in mind if one drive goes, you can lose all your data on all the other drives. If you have multiple drives that are ultra SCSI you might wish to get more than one SCSI card so that you can try to fill up that bandwidth. Realistically 20MBps is SLOW. Run one of the speed test programs on your machine and you'll see what I mean.

Most of this debate only works when you're talking Ultra2+ SCSI and with multiple drives in RAID. Otherwise the ATA will be faster.

[ferg]

Thanks much, i will just use them as storage then.

[awcopus]

Awesome display of knowledge here. Here's a question: Is there currently a product on the market that enables a Mac user to buy EIDE drives and place them in an external enclosure and use them in a JBOD or RAID configuration with a Mac via a PCI card that is essentially the equivalent of an ATA/133? Via a PCI-X card (compatible with the G5)?

I have the Sonnet Tempo ATA/133 in a Quicksilver and use four WD 200GB internal drives. Would love to be able to achieve the same throughput as I do with this configuration using a virtually identical external configuration with the G5. Don't want to use Firewire (400 or 800) because it's too damn expensive and, as I understand it, not as fast or stable as the ATA bus for video editing.

Thanks in advance for any thoughts or knowledge you can share on this topic.

[SMacTech]

Originally posted by awcopus:
Awesome display of knowledge here. Here's a question: Is there currently a product on the market that enables a Mac user to buy EIDE drives and place them in an external enclosure and use them in a JBOD or RAID configuration with a Mac via a PCI card that is essentially the equivalent of an ATA/133? Via a PCI-X card (compatible with the G5)?

I have the Sonnet Tempo ATA/133 in a Quicksilver and use four WD 200GB internal drives. Would love to be able to achieve the same throughput as I do with this configuration using a virtually identical external configuration with the G5. Don't want to use Firewire (400 or 800) because it's too damn expensive and, as I understand it, not as fast or stable as the ATA bus for video editing.

Try this place for external RAID solutions. Get a good PCI SCSI card which can interface to a RAID box using IDE drives, that can be used in your G4, G5 or any PC. The above may be too pricey for you. A google search brings up many other solutions too.