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IDE, SCSI And Recording Everything
Raju writes: "For many years we were told that SCSI is superior to IDE. I always made my systems with SCSI and the others in the household got el-cheapo IDE disks. In the past SCSI beat IDE hands-down but now according to Simson Garfinkel, "today's IDE drives are significantly faster than SCSI drives". In the article at O'Reilly Network he talks about the tests they had run for storage of network data on disks. In the light of this article does anyone see any reason for going with SCSI in a desktop machine? For servers with heavy disk usage patterns it might be different due to command queuing." Disk types aren't what the article's really about, though -- it's a top-level look at network forensics (including advice on building a traffic-analysis system), and makes some interesting points about the unbalanced growth of storage and bandwidth.
The article's authors needed a way to store large amounts of network log data quickly - they're trying to capture packets in real time. For that kind of straightforward use (large volumes of data, only one user, no simultaneous read/writes) it's easy to see why IDE is more cost-effective and speedy, as the article states. However, when you add multiple users trying to write multiple drives simultaneously, the story changes, and the article simply doesn't address that.
What's your damage, Heather?
I agree that it's the reliability that's the big factor.
Ever try to add 8 IDE devices to a system? With SCSI it's a snap as long as your power supply is large enough.
I think this is very application specific though.
As if the tens of thousands of times this has been hashed out weren't enough already...
The question of IDE vs. SCSI is not (or should not) be about speed. Really. There are nice, fast drives in each camp. If speed is all that matters to you, go with IDE, it'll be a lot cheaper.
So are there any advantages to SCSI? Sure. But not for the majority of people. SCSI's beauties are:
- You can hook a LOT of drives to one controller
- You can hook most any kind of device to the controller
- You can hook devices up both inside and outside of the case
- You can use much longer cables
- When the controller is waiting on one command, it can issue other commands while it's waiting
SCSI was designed for systems where you would either have many, many devices connected to the controller, or where many different processes (or users) would be accessing the hardware simultaneously - and in either of those situations, it *does* perform better than IDE. However, the portion of systems that will actually enter into that area are very, very few. In general, "if you have to ask, you don't need it."
As for straight speed, if you're looking for all-out throughput, don't rely on a single drive, get a RAID array - be it IDE or SCSI. By getting a faster drive, you can increase your throughput by what - 10%? 20%? A two-drive array will nearly double your throughput, and with quality controllers, it's fairly linear up through three to five drives - again, depending on the quality of the controller.
steve
Oh, you're not stuck, you're just unable to let go of the onion rings.
The main SCSI advantage is not that it's faster in I/O than IDE (although it used to be). The really big advantage was that (and I think still is), that on a server under heavy memory and processor load, SCSI will outperform IDE because most of the logic is moved off the CPU and onto the SCSI card. So when the CPU is pegged, IDE crawls, but SCSI keeps on chugging.
I think one of the big things is that processor speeds have kept on shooting up, meaning that while IDE has been considered a serious contender for small to mid- sized servers increasingly over the past few years, it's now becoming much more plausible to use it on higher scale systems.
That's probably true. For example, you can buy a n 80GB western digital 7200RPM drive for $150. That is $1.88/GB. The only 7200RPM SCSI drive made these days is the Seagate Barracuda, which is $300 for 36GB: $8.33/GB.
That really isn't the point of SCSI though. I'll accept that IDE wins on a money-per-GB basis. But, IDE has a performance ceiling that SCSI doesn't have. You can't get 10000RPM and 15000RPM drives for IDE at any price, period.
There is a point, when building RAID systems, where SCSI exceeds IDE in the $-per-I/O-per-second metric. In desktop systems, you probably won't exceed this point. But if you intend to have stripe sets of 4 or more disks, SCSI will win the price wars again.
Anyway it really isn't a matter of SCSI being expensive and IDE being cheap. It's the drives that are expensive/cheap and it simply works out that expensive drives get SCSI connections and cheap drives get IDE connections.
P.S. Have fun trying to get you 4-disk IDE RAID all within 18 inches of your IDE controller :)
My vote is for the low-CPU usage of scsi devices. My hardrives, DVD drive, CDROM, and CDR are all SCSI.
... start copying around movie files while it does this, and you'll become a SCSI fan real quick.
:| It really does make a difference, though lately IDE has been too cheap to ignore.
I can run three instances of grip and rip/encode from all three drives simultaneously. Desktop still runs like a champ, it doesn't bog down. Rip from one IDE drive and it does ok
Sure, I may pay $400 for an 18GB SCSI drive, but it's worth it.
I agree.
However, I want to see not one, but eight IDE drives outperforming eight SCSI drives doing heavy I/O. That's the crux of the question for servers. For desktops, just go IDE and that's it.
I wish it were possible to moderate the initial article submission as being off-topic, because from what I have gathered from actually reading this excellent article is that the individual who submitted this story completely overlooked the primary topic on which the article was written...
The speed comparison of SCSI vs. IDE was most certainly referenced within the story context of the story; however, that was by no means the intended takeaway that the author had for his readers - it was but a supporting factoid of his other conclussions and thoughts. The article was a very written analysis, history and summation of the practice of Network Forensics. While it did cover a wide range of technologies (including hard disks) that aid in the collecting of such forensic intelligence, by no means was his observation of the increased speed of IDE drives intended to monopolize the reader's attention or be the central focus!!!
Even worse, the majority of posters have (unsurprisingly) focused on everything but the article's intended subject matter. Now ensues the typical flame-war of people supporting their preferred technology instead of having intelligent discourse concerning this exciting and evolving new field of I/T security...
Oh well...if you can't beat them, I suppose you might as well join them! For the record, my vote remains with the tried and true performance and quality of SCSI...
Beer is proof that God loves us and wants us to be happy. -- Benjamin Franklin
That's only true if the program is doing disk I/O asychronously. If your program is doing I/O inline with its execution, it will be paused just as long reguardless of where the disk I/O computation is being done.
personal attacks hurt, especially when deserved
IDE has gotten a lot faster these days but there are still many flaws.
For one, most of the ATA133/ATA100 is a lot of hype. On long transphers (or any transphers that exceed the cache size of the drive) I have yet to see an IDE drive break 30-40 MB/s. In fact, testing an "ATA133" drive on an ATA133 controller vs. an ATA100 controller I saw no gain in speed. There was a gain from ATA66 because the ATA66 bus can't quite sustain 30-40MB/s constant.
Which brings me to another point, like all buses, the 66/100/133 is the peak allowed, it is usually not nearly that fast.
The drive speeds could be higher on IDE. You can get some top notch SCSI drives that run at 15,000 rpm. The best you find with IDE is 7200rpm. The drives would obviously be a little better at filling the bus if they had faster motors.
The IDE bus lacks any intelligence. It is the intelligence you are really paying for on SCSI. The command queues, multitasking bus, ect. ect.
Lastly, SCSI drives are obviously way more expensive, as are there controllers. Of course you are getting a higher quality (read=better built, not faster) product.
Basically what it comes down to in real world performance is no matter what you choise, IDE or SCSI, your disk drives will be the biggest bottleneck in your system by a long shot. If you run a single drive system, or have enough buses so you don't share them SCSI doesn't really provide enough to justify the cost on a desktop in my opinion.
Can someone explain me why SCSI drives are more costly than IDE? I believe (I might be wrong) that many IDE and SCSI drives share the same mechanics and thus, its the electronics that change.
I can understand that 80's and 90's that SCSI electronics were expensive, but I would have expected that electronics prices would fall. How complex is a SCSI controller? Does it have a chip running at 600Mhz or something?!? (Guess not).
Any input about the reasons why SCSI $> IDE is welcomed.
Remember the year 2000? They promised us flying cars. They delivered the PT Cruiser...
Beta is technically superior to VHS.
Novell Netware is technically superior to Windows NT.
SCSI is technically superior to IDE.
Does any of this matter to most of the market? Not really, since most people look primarily at up-front cost. I've been telling my customers (mainly small businesses) that mirrored IDE drives are the best value for general purpose data storage. The gap has narrowed; IDE definately makes more sense for most people (and even most servers) these days.
If I were specing out a system for high-end video editing, or a system that absoulutely had to process thousands of transactions a second, or a general purpose file or e-mail server that supported thousands of users, or a GIANT SAN, I'd go with SCSI. SCSI shines in really big storage pools, or in places where you absolutely need the fastest possible speed. But for most things, IDE undercuts SCSI by a longshot.
That said, there is one major problem with IDE, and it's not bandwidth (as most "higher-end" IDE-RAID controllers (such as some of the new ones by Adaptec) have multiple channels for multiple drives) - it's lack of VERY standard chipsets & APIs needed to access IDE block devices. The original spec has been hacked onto so many times that you're really at the mercy of the manufacturers' drivers for any "sophisticated" IDE implementations. This has gotten me into trouble several times. SCSI drivers tend to be more plentiful than high-end IDE drivers, and the testing cycles seem to be better because OS vendors actually care about them.
But again, people who buy IDE just on the technical merits of it may as well throw their money away. I wish the situation were different, but I don't think it will change unless drive vendors DRASTICALLY lower SCSI drive prices. Right now they're getting away with charging lots of extra dough simply because managers are hearing "SCSI is way better!" from their employees when purchasing hardware. That may have been true a few years ago, but it'll take a few years for the general consensus to swing in the other direction. (I really, really like SCSI too, and I think IDE sucks as a technology... but money talks) :(
I agree that 3ware makes excellent products. One slight nitpick though. The Adaptec 2400A beats 3ware's 7450 in some RAID level and test combinations, though it is limited to 2 channels whereas 3ware offers the 7850, with 8 channels.
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IDE drives are fine in a desktop machine. It isn't likely to be heavily stressed and any reads and writes are likely to be from a single application at a time and a single user at a time with a CPU that is typically 99% idle. Such a user doesn't need the benefits of SCSI and the additional costs that the marketing people add.
If however you have 100 people all accessing different pieces of the disk, some reading some writing then IDE will just not cut the mustard. It requires too much CPU involvement. With SCSI the CPU just says here you handle this to the SCSI interface and gets on with something else instead. In addition, with SCSI I can have 15 devices on a single bus, with IDE, I can have 2.
So basically:
SCSI = scalability & heavy loads.
IDE = low cost & single user access.
Use the one appropriate to your application. For most people that'll be IDE, for other people chucking a lot of data around and lots of processes doing different things, SCSI would be better.
Just a quick rant about laptops. People think that a 1GHz laptop is as fast as a 1GHz desktop. It isn't. The laptop disks are designed with power management in mind and are often significantly slower than normal IDE even. So if your managment think that everyone should have laptops, tell them not to complain when their Oracle client runs like shit.
Government of the people, by corporate executives, for corporate profits.
IMHO, the SCSI bus system is better than everything IDE/ATA can offer to date. It's not necessarily the devices that need to be put up against each other. Most recent SCSI disks in "acceptable" sizes are so expensive that you can easily build a RAID system from IDE disks for the same or even lower price. However what's really bad about IDE is the short bus. Face it, length and size do matter in some cases.
You can have a 12m LVD-SCSI bus with 15 devices plus controller running at full speed. But that's not desktop. You'll have trouble just cramming the disks in your average-sized tower, and you still need one or two additional PSUs to get them spinning. And now you take the sucker out for a LAN; but don't forget calling your chiropractor and get a reservation for the next two weeks straight.
Then there's IDE. With todays U-ATA133 specs you're limited to, like, 50cm bus length. Heck, that's about the height of a midi-tower! But it gets the job done. But no external devices for you, sorry. And you're down to 4 devices on your average motherboard, but most users can live with CD-ROM, CD-RW and one or two disks. With onboard RAID controllers coming up, there's an additional four disks possible and you can even plug in a separate DVD drive. You don't need a nuclear plant to get it running, you have lots of storage for a desktop machine and you can still carry it around. Perfect.
To sum it up, I think SCSI is still great, but it's losing on the desktop nowadays. The disks might last longer, it might be more flexible, but in the end, it's way too expensive and overkill. And then there's serial ATA on the horizon.
Fight hunger. Filet a politician and send him to a 3rd world country of your choice.
right on par.
...chirp chirp chirp...yep, it's pretty damn quiot out there. sure you have a few companies out there touting their ide hardware raid, but it's not really an option, again imo.
that statement is somewhat simplified....but i'll agree.
i like ide in workstations because it's 75% the performance for about 1/2 the price.
if money is no object, then a little over a grand will get you a nice pair of 15,000rpm top of the line drives plus a controller.
for someone who builds $4000 workstations, it's no big shit.
if you are building a game/web/general purpose athlon system for $600, it does not make any sense to spend gads of cash for scsi.
servers--well that's a whole different subject.
scsi hardware raid, imo, "just works"
ide hardware raid,
finally, i don't deny that ide has made huge gains. i used to hate using ide drives, they just plain sucked. now, i think they are decent.
but they aren't that great. i would call them "satisfactory".
Errr - from your own admission, there are two advantages to scsi:
1) faster drives - manufacturer unwillingness or what not. This is because Joe Blow would rather have a 60GB drive for $180 than a good 18GB for $300.
And:
2) More drives.
Basically, SCSI drives are better drives.
First, bigger caches.
Second, better bandwidth. SCSI is going to 320MB/s. Where is IDE - 133MB/s?
Third, lower latency.
Fourth, you can use several drives better.
To state simply - SCSI is a better engineered interface. IDE is designed to be cheap. No matter how many excuses and FUD is thrown, it is the truth.
No, I don't trust in god. He'll have to pay up front, like everybody else.
SCSI as a protocol is far superior (in terms of performance design, connectability, intelligence, and fault tolerance/scalability) than IDE (which essentially acts as a glorified signal converter). Regardless of what any benchmarks attempt "prove," SCSI does not present an overhead which inherently degrades single-user performance. Given the same drive mechanics and comparitive channel rates (ie. 80mb/sec - 160mb/sec LVD, or FC), SCSI disk performance will meet or exceed IDE disk performance, for any given single user application.
When you begin to involve more complex and real-world use of disk drives, the difference becomes tremendous. Think faster disks (15k rpm Seagates), switched fiber interconnects (running >200mb/sec), spindle synchronization, and intelligent command queueing. The added cost (which is usually insignificant compared to the cost of downtime, delayed I/Os, and maintenance) becomes a non-issue.
99% of the high performance computing industry chooses SCSI over IDE as their block device interface, time and time again, and there is a reason. To do so otherwise demonstrates a fundamental misunderstanding of storage interface technology.
A government is a body of people notably ungoverned - AC
Are there 15,000 RPM EIDE drives? I don't think so; the fastest I have seen is 7200 RPM and they are rare. What is the MTBF of the drive? EIDE may be faster at burning out. IBM gives a usage cycle of their drives that indicates they are designed for desktop use, not server use. This is usually reflected in the warrantee periods of the drives. 5 years is standard for SCSI, 2-3 for EIDE.
There's more !/$ on EIDE than SCSI, but the performance and reliability isn't there.
In any case, it's a matter of the appropriate use of technology.
Yet again, Simson shoots his mouth off without knowing the full story. Or maybe he does, and ignored it.