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SCSI3 15K RPM HDD Advantage over 10RPM SATA Drives

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February 17, 2007 4:03:43 AM

I've been discussing this issue with a friend who is hell bent on getting himself an all new hardcore system with SCSI3 15RPM HDD to have "The" Very darn best performance ever for everything he does for his home PC basically, programming, playing games, watching movies and such.

I've been looking around the net and yeah SCSI3 has better theoretical performance and it does seem to reflect in real world application in a server and time-critical situation but I was wondering this: Is it really totally that much faster for home use ? what could justify paying so much for such a setup give the fact it will probably not be used as a RAID ( Only one 15k RPM Drive ). What could be the reasons to justify buying a SCSI card and a SCSI HDD for a home computer versus the more mainstream and less cheaper SATA solutions like the WD 10k Raptor drives.

If anyone has a good explanation or some sources I could verify I'd love to hear about it so that I can look it up in bigger details

Thanks a lot for your time and responses !
February 17, 2007 12:52:39 PM

Are the 15K RPM drives faster? Yes. They have a faster seek time & lower rotational latency time than 10K RPM drives.

However, SCSI's main advantage is the way the firmware is designed. The drive is really designed to maximize the IO transactions per second (IOps). This makes the drive excellent for multi-process, multi-user random reads, like would be experienced on a file server or database application.

It doesn't do too much for it in single-user environments.

Unless you were pounding a workstation with multiple random IO requests from several opern programs, the speed advantage of the 15K drive would be less than you would think.

It would be interesting to pit one SCSI 15K drive vs. 2 Raptors in a RAID 0 against the IOMeter workstation benchmark and see how they perform. They might be kind of close. And 2 Raptors in a RAID 0 might be cheaper.
a c 105 G Storage
February 17, 2007 2:51:51 PM

Speed is speed and 15k, all things being equal, will always outperform 10k. One thing to note is that as new HD technology is introduced, we are going to see it first on SATA drives before we see it on more expensive SCSI drives. I am real anxious to see what Seagate does with its new 2.5 " SCSI drives.

Last time I looked 15K SCSI jobs were just a hair under the 100MB/s number at about 97-98 at the outer end and 75 at the inner. The Raptor is 88/60. Seek time on a 15k drive is about 5.5 secs whereas 8.0 on the Raptor. Another advantage to SCSI is that it offloads the I/O management overhead from the CPU. Of course s vendors optimize the I/O foir certain uses, this may or may not favor what YOU want to do with the drive. If you are a gamer, check here:

http://www.storagereview.com/articles/200601/WD1500ADFD...

The Fijitsu MAU1347 is about 18% faster than the Raptor in Far Cry but the Raptor beats its nearest SCSI competitor by 9% in Sims. The Fijitsu leads by 14% in Warcraft.

The biggest problem with SCSI is that manufacturer's are not going to invest time in optimizing their drives for single user performance. It's just not their market as they are convinced there is not enough money to be made. As a result, the gap between SCSI and SATA performance is continually narrowing.

And yes, twin RAID 0 Raptors should outperform a single 15k SCSI but with the investment in SCSI controller already made, the 2nd SCSI HD can be as easily justified and twin 15k's will outperform the twin Raptors.

Can the expense be justified ? If you can justify a core duo extreme and SLI, you can justify just about anything.
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February 18, 2007 2:07:08 PM

I've also been rooting around looking for people's opinions on this topic.

A lot of people won't purchase a scsi due to the price of admission. I am considering it since they are built well. I have some old 10k scsi drives from 1993 or so and they still run fine, at least to my knowledge. I can almost justify paying a good deal more if I know the drive will last much longer than a standard desktop drive.

I was considering using two Fujitsu 74 gig drives in raid 0. That would run about 900 dollars though and the question is, can that be justified?

Maybe a better question is. 2 raptors vs 2 scsi both in raid 0. Is there really going to be THAT much of a difference? Something tells me that on day to day normal computer work, no. I would probably benefit more-so from a faster CPU or more ram and just do 2 raptors.

I guess I came to my own conclusion. :lol: 
February 18, 2007 2:56:34 PM

15k RPM SCSI (Preferably SAS) drives wont have Workstation optimised firmware, but their raw performance should overcome that.

However, 2*150GB Raptors in RAID 0 will be much cheaper, and about the same speed (slower seek, faster sustained read/write) as than a single 15k. Hell you could easily have a 3 drive RAID 0 array for the price of a SCSI setup.
February 21, 2007 5:54:59 PM

I know for sure that the system will not have an extreme processor or even the latest video Card in SLi. This harddrive will be used for simple use as mentioned in my first post. We have also discussed WinRAR compression/Decompression supremacy which I was told was HDD intensive while I believe is either CPU or CPU+RAM intensive.

I have been asking myself... what real time difference does it make to have let's say one raptor vs one SCSI ? Does everything seem like a magic improvement of speed or is the 50% theoretical performance gain a 15K RPM drive have over a 10K RPM Drive simply marginal unless I end up having hundred of people seeking data on the drive.

Will it make games or applications load really that much faster or are we talking about something that isn't really noticeable ? Will Winrar take half the time to compress/decompress files on the same system ? Will Windows' Page File be that much faster to access thus making windows faster to operate ?

In my opinion there won't be any kind of real major jaw dropping improvement. Yes the drive is faster and it will result in a faster response and performance but i'm a patient person I can wait for something to load. some people seem to be totally irritated by a program taking 2-3 seconds to load.. it should load instantly with the content already loaded like magic.

I've seen very often and also on this site's reviews that the bottleneck of the PC is the Harddrive but I don't think there going SCSI will eliminate the bottleneck but by how much will it really decrease ?

My examples here are somewhat exaggerated to try to explain my point. I hope I can get some good feedback from this to further enhance the discussion! :) 
February 21, 2007 6:29:50 PM

WinRar is mostly CPU intensive.

Simply check the CPU benchmark tests.
You will find that this scales very much along the lines of the CPU speed.
The HDD plays very little role.

The faster HDD will help in OS Boot times, Game Load Times, etc.. etc...

If you want your game to RUN faster, then you are better off with a FASTER CPU and FASTER GPU.

Personally I would only start looking at SCSI drives after you have maxed the GPU and CPU. Then look towards raptors and if you still have needless money go for the SCSI drives.

If you want REALLY fast game peroformance, though, look for somethink like a RAM Drive with about 8gb of space. You could install your game to this and blow away the performance of even SCSI. This would not help with OS boot or other things, but if you are one of those folks who wants that .01 second advantage entering a new region in a game this may help.
February 21, 2007 6:47:13 PM

the REALLY HUGE cost is not worth it.

Remember:

- SCSI is 320MB/s maximum, shared for ALL the drives in the same cable.
If you have many drives you're bottlenecking. (unless you use SAS)

- good SCSI raid cards are expensive

- good scsi drives are crazy expensive
(over $800 for 300GB on 10k rpm as I remember)

- good scsi cable is expensive (yes, you need a good cable with a terminator to avoid problems)

I tried using an LSI Megaraid 320-2 with 256MB cache and 4x 73GB seagate chetaah drives once for my gaming rig, and performance against fast sata raid was not that great (not worth the tons of extra $$$)

also:

- scsi cables are BIG, remember trying to do cable management with you IDE/PATA hdds? this is 2 times worse....

- make sure the scsi card is PCI express and you have a free 4x or 8x slot they need.
Dont use a normal PCI slot since they may bottleneck (that why old high end scsi cards are the big pci 133mhz)

- 15K gets REALLY hot, make sure you have them really well ventilated


And if you have that lot of money to buy it anyway, send me a couple os $100's :) 
February 21, 2007 7:10:48 PM

Quote:
What could be the reasons to justify buying a SCSI card and a SCSI HDD for a home computer versus the more mainstream and less cheaper SATA solutions like the WD 10k Raptor drives.

Thanks a lot for your time and responses !


All other things considered equal, a 15,000 RPM SCSI drive would be 50% faster than a 10,000 RPM Raptor and a little over 100% faster than a common 7200 RPM drive. Further, since SCSI drives are normally commercial quality rather than for home use, they will last years longer.

That said, they are vastly more expensive, either requiring adapter cards or a special motherboard that is more expensive then is normally used in the home. They run hotter due to their speed, so must have their own fans for cooling. Since the adapters take up exptra space, you must have a large case to fit everything in.

If you both have the money to pay for a SCSI drive and have the either the great need of one or the great ego that demands the fastest drive available, then go ahead and buy one. Otherwise, get a Raptor, which is a bit expensive but not nearly as much so as SCSI, and have a faster hard drive than most people use.
February 21, 2007 11:00:34 PM

FYI Speed isn't speed and "all things" are never even close to equal.

Hard drives are a lot more complicated than people realize, and unless you are an engineer at a HD manufacturer any notion that you may have about how a hard drive actually works is dumbed down and over-simplified.

Point is that a HD doesn't just receive a data request, move to the right track, wait for the platter to spin to the right location and then read the data as it passes under its heads in a straight forward fashion.

No more than a modern CPU executes one instruction at a time in the order specified by the compiler.

Thats why you can just look at a few performance metrics and then accurately predicts which hard drive will perform better at a given task.

Just like CPUs, with Hard drives you have to look how the drive actually performs under a variety of tasks and then try to guess which will work best given the way you expect to use it.
February 22, 2007 12:12:42 AM

Quote:
FYI Speed isn't speed and "all things" are never even close to equal.

Just like CPUs, with Hard drives you have to look how the drive actually performs under a variety of tasks and then try to guess which will work best given the way you expect to use it.


I realize that there are various differences, which is why I used the phrase "all things being equal". They aren't, but without a lot of charts and accompanying explainations, I don't see any practical way to differentiate among drives. I was trying to address the main question of the OP, which was to relate theoretical performance to real world performance, and in the real world senario, I believe a 10,000 RPM Raptor would be far more usefull than a 15,000 RPM SCSI drive. Perhaps I didn't explain my thoughts well enough. If so, then i'm at fault.
February 24, 2007 4:42:20 PM

Quote:
here is an interesting article just about this

http://www.pugetsystems.com/articles.php?id=19


Very interesting comparisons. Thank you for finding those charts. They do indeed show a Raptor as being just as good as, or even better than. a SCSI drive in almost everything. Now I've learned something to keep in mind about hard drives.
February 24, 2007 5:02:14 PM

Quote:
- SCSI is 320MB/s maximum, shared for ALL the drives in the same cable.
If you have many drives you're bottlenecking. (unless you use SAS)


There are cards with multiple channels that go around this bottleneck. A dual channel SCSI card will give 640MB/s max which is plenty

Quote:
- good scsi drives are crazy expensive
(over $800 for 300GB on 10k rpm as I remember)


I've seen good 15k drives on ebay for less than their raptor counterparts(for the same size drive) I saw a pair of 74GB's go for like $120 last night.

Quote:
- good scsi cable is expensive (yes, you need a good cable with a terminator to avoid problems)


Agreed 100%, however, SCSI cables are a million times more sturdy, I have tons of SATA drives and if I bump my computer one will always come loose, this happens constantly. SCSI cables have a much firmer connection all around, and it's worth the cost increase to me.

Quote:
I tried using an LSI Megaraid 320-2 with 256MB cache and 4x 73GB seagate chetaah drives once for my gaming rig, and performance against fast sata raid was not that great (not worth the tons of extra $$$)


In my experience, SCSI is way faster, I do a lot of multitasking and that's where it shines. I've used many SCSI setups, on my last one I used 3x 74GB 10k IBM drives on an Adaptec 2100S with 256mb cache. I sold that setup to go sata, big mistake.


Quote:
- scsi cables are BIG, remember trying to do cable management with you IDE/PATA hdds? this is 2 times worse....


This argument holds no water at all. SCSI cables are much thinner than IDE. Also, you can chain several drives together with a single cable with SCSI, try that with SATA. I have a huge mess of SATA cables now compared to a single SCSI cable like I had before that was much more manageable.

Quote:
- make sure the scsi card is PCI express and you have a free 4x or 8x slot they need.
Dont use a normal PCI slot since they may bottleneck (that why old high end scsi cards are the big pci 133mhz)


This is very true, I had a friend get a massive SCSI array and he put it on 33/32 PCI. Needless to say he was less than impressed

Quote:
- 15K gets REALLY hot, make sure you have them really well ventilated


Very true, I've been burned by SCSI drives when the fan died.

SCSI is way more reliable all around, they're very tough drives and the cables stay secure. Also, SCSI drives are the fastest drives out there, if you need hardcore speed they're the only way to go.

With that said, it sounds like for what he's using it for a single raptor would do just fine. But I see a lot of people saying bad things about SCSI that simply aren't true.
February 24, 2007 5:31:46 PM

Tell him to get SAS as that is the new scsi.
there are good hardware pci-e sas / sata raid card out there
February 24, 2007 5:41:37 PM

Quote:
Can the expense be justified ? If you can justify a core duo extreme and SLI, you can justify just about anything.

:D  :D 
Post of the day material !!!!!
February 24, 2007 6:13:22 PM

Quote:
Tell him to get SAS as that is the new scsi.
there are good hardware pci-e sas / sata raid card out there

SAS still uses SATA cables which are awful, and it's really no better than SCSI, other than perhaps being more future proof.
February 24, 2007 8:11:25 PM

Quote:
SAS still uses SATA cables which are awful, and it's really no better than SCSI, other than perhaps being more future proof.


Well, the SAS cables are much better than the old combersome SCSI cables. And in reality SAS is much faster than SCSI U320 and have the added advantage of being able to mix SATA and SAS drives for the best combination of performance and capacity.
Old SCSI is dead, SAS just have too many advantages. Look at this test of a high end disk system (12 disks in RAID!), comparing SATA I and II, SCSI, and SAS drives. SAS wins hands down.

http://www.anandtech.com/IT/showdoc.aspx?i=2919&p=1

Yes, SAS is expensive, but if you pay for SLI, quad core and what have you not, why not get the best disk system, and that is SAS.
I don't understand how you can spec a 7000-10000 USD performance system and not include a SAS RAID controller.
February 24, 2007 10:07:36 PM

I stand corrected on there not being many advantages to SAS. I still don't like the cables, I have 8 sata drives, 8 seperate cables is much more difficult to manage than one single ribbon cable. Mixing and matching SATA and SAS would be a huge advantage though.

Quote:
Yes, SAS is expensive, but if you pay for SLI, quad core and what have you not, why not get the best disk system, and that is SAS.
I don't understand how you can spec a 7000-10000 USD performance system and not include a SAS RAID controller.


I've always wondered the same thing. I mean why go overboard on the CPU and video card and then cheap out on the hard drives. Plus, if I'm gonna pay $10,00 I want some redundancy.
February 24, 2007 11:00:38 PM

SAS 4tw.

You don't have to have lots of cables, there are "multilane" x4 cables about, which are basically 4 cables in one. This allows the controller to connect 4 channels via a single cable to an SAS backplane, upon which 4-8 drives can be mounted in their removable caddies.

Thats 1200MB/s of bandwidth, waaaay more than U320
a c 154 G Storage
February 24, 2007 11:46:50 PM

I have tried both. The short answer is that a single raptor, and a single 15k scsi drive will both perform about the same in a single user desktop environment.. If there was a difference, it did not jump out at me. I bought a 15k fujitsu and an adaptec pci scsi card on e-bay. They are relatively cheap if you want to try. 15k scsi drives will only use up about 80mb of the 160mb available bandwidth of a normal pci slot, so two drives would not be too many. The raptors make up for the slower transfer speed by better use of their 16m buffer. I think they will anticipate reading more of the track into the buffer. A scsi drive is optimized for random seeks, the main thing in a server farm. Go to storagereview.com , and look at the single user workload benchmarks. By the way, they do not find any benefit in performance for raid-0 in the single user desktop environment.
There is a decided advantage to the newer adfd raptors with the 16m buffer, as compared to the original raptor.

My 2cents: Stick with a single adfd raptor if it will hold all your data. When the new hybrid hard drives come out, look at them.
February 25, 2007 12:41:15 AM

As Geofelt above said, the difference in speed won't be very significant.

Your friend should consider the amount of money he is going to spend.

Pressuming he is on a limited budget - as most of us are - he will be much better off spending the money on additional memory than on SCSI.

Additional memory will cut down on the number of I/Os the system has to perform and, there is no faster I/O than the one that doesn't happen.

HTH
February 25, 2007 12:42:09 AM

PCI 33MHz 32bit is 133MB/s, and thats shared between all the PCI slots.

A PCI sound card or other device will therefore fight for bandwidth with your RAID array, and twin Raptors can hit more than 150MB/s in RAID 0, so would be limited on PCI.

PCIe SCSI or PCI-X SCSI is the only way really.
February 25, 2007 10:17:50 AM

Quote:
I have tried both. The short answer is that a single raptor, and a single 15k scsi drive will both perform about the same in a single user desktop environment.. If there was a difference, it did not jump out at me. I bought a 15k fujitsu and an adaptec pci scsi card on e-bay.


But that was old parallel SCSI, which I no longer recommend. Even though neither SCSI nor SAS harddisks use up the theoretical bandwidth of their interface, SAS has been uptimized both as a protocol and on the disks, to deliver much better performance than the old SCSI. Look at the test I cited in an earlier post. Yes, it is not a single user, one drive configuration, but in that test (with the same SAS controller), SAS wins clearly over old SCSI and SATA. Only on one test the big cache on the Raptors gives it an advantage over SAS.

My own experience from work with two identical HP xw9300 workstations, one with SATA WD Raptor (74GB version), and the other where I went all out and got two 15k parallel SCSI drives (not in RAID, and there were no SAS option for the xw9300 at that time :(  ), shows that in workstation use only got a 10% to 20% performance boost over SATA raptors. I didn't do formal testing, just measuring Windows startup, Photoshop load image times and general disk search.
What the results for SAS on a workstation would be, I don't know, but if the tests from anandtech is any indication, it looks worthwhile to try on a highend system.
March 8, 2007 11:53:20 AM

Another factor that will limit overall data throughput is the interconnect between the north bridge and south bridge on the motherboard. Most standard motherboards have PCI slots and ATA interfaces connected to the south bridge chip set and the memory interfaced on the north bridge set. This means to get read/write your data from/to the harddrive into/from memory it must cross the 256KB interconnect between the north and south chip sets. Some of the newer server and workstation motherboards have the PCI-Express slots interfaced directly on the north bridge chipset and will not have this bottleneck. You will have to look at the motherboard schematic to determine if you have this limitation. Some vendors print a high-level diagram in the users manual.

I'm a big SCSI fan, but due to costs and the very little extra performance improvement you get with SCSI, I've switched to SATA for my new machines. :?
March 8, 2007 1:39:00 PM

Quote:
Another factor that will limit overall data throughput is the interconnect between the north bridge and south bridge on the motherboard. This means to get read/write your data from/to the harddrive into/from memory it must cross the 256KB interconnect between the north and south chip sets.


It's not a problem with any newer chipset. For example the P965 chipset has a 2GByte/s transfer rate between north and south bridge. That is certainly not a bottleneck. I don't know where you find the 256KB (Kilo Byte per second????) interconnect you mention.
March 9, 2007 1:22:30 AM

I stand corrected. The last time dug into the specs which was about three years ago, I ran into this 266MB/s limit and was frustrated. I'm glad to see that this is no longer a bottleneck. Many of the Intel chip set designed in 2005 or later use a Direct Media Interface (DMI) between bridges that have a limit of 2GB/s (1 GB/s in each direction). I'll check the specs before opening mouth next time. :oops: 
March 9, 2007 9:31:29 AM

The NB->SB link can still be an issue.

With alot of Crossfire/SLi boards, definately those based on nForce 680 and nForce 5, the second PCIe x16 slot is on the southbridge.

As such, the NB->SB link (in nVidias case, Hypertransport) can be pretty saturated before you start with a large RAID array.
March 9, 2007 10:58:06 AM

Quote:
The NB->SB link can still be an issue.
With alot of Crossfire/SLi boards, definately those based on nForce 680 and nForce 5, the second PCIe x16 slot is on the southbridge.
As such, the NB->SB link (in nVidias case, Hypertransport) can be pretty saturated before you start with a large RAID array.


That is certainly a very specific situation. It's only the rather special combination of high resolution SLI, nVidia chipset and a high end RAID setup (i'd say with at least 4 drives). Anyway, two graphics cards using 100% of the PCI-E 16x busses, will overwelm the CPU's FSB.
So it's a highly theoretical situation using a very specific combination of products under which it might actually be the north-southbridge interconnect which is saturated before the FSB.
On platforms with a faster FSB such as the Intel 5000X chipset, there are only one PCI-E 16x, while a secondary SLI graphics card can be placed in a PCI-E 4x connector. By the way I suspect that the FB-DIMM memory limits the performance more than any interconnect ever could.
March 9, 2007 12:58:59 PM

nforce 680 amd is used on the 4x4 system and it has 1 Full HT link form the cpu to each chipset. Nforce pro set up the same way there is even a older nforce pro system that has a ht to pci-x chip as well. Newer one just use 4 pci-e lanes for pci-x and some have a raid chip on 4 or 8 pci-e lanes on board.
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