EggXpert

As most of you may know, SCSI drives are generally the fastest drives on the market (and the most reliable) due to their use in high-load, high utilization, mission critical servers. I've been asked by someone to write up a guideline as to how to get your rig set up with SCSI, because I claimed that a 10,000 RPM SCSI drive + cable + terminator + controller could be had for as much as an identically sized 10,000 RPM Raptor and that you can buy a 15,000 RPM SCSI drive for less than $1 per gigabyte. 

There are 4 things you'll need to run SCSI on your computer. 

1.  A drive

2.  A controller

3.  A cable

4.  A terminator

But before we begin, you need to be familiar with a few concepts.

SCSI-320 is currently being phased out in favor of SAS (Serial attached SCSI), similar to how IDE is being phased out in favor of SATA. However, the performance SCSI-320 is comparable to SAS. When buying a drive or controller, you have the option to purchase either controllers and drives supporting SCSI-320 or SCSI-160 drives. SCSI-320 is backwards compatible with SCSI-160. SCSI 160 can transfer 80MB/sec full duplex (read and write) between the drive and the controller, while SCSI-320 can transfer 160MB/sec full duplex. The fastest SCSI-320 drives you'll find won't exceed 95MB/sec in read speed.

Now to understand how drives read data, you have to understand the concept of circumference on a drive. If a drive has a circumference of 2 inches at the center and spins at 10,000 RPM, you will be able to access 20,000 square inches of area per minute. If the same drive has a circumference of 4 inches at the very edge of the drive, you will be able to access 40,000 square inches of area per minute, which means that data written to the outer edge of the drive can be read faster than the data written on the inner edge of the drive. With traditional 7200 RPM hard drives, the platters are relatively large. However, 15,000 RPM drives have much smaller platters, allowing a much smaller difference between the slowest and fastest write speeds of the drive.

Traditional 320GB 7200 RPM drive:

300GB 15,000 RPM SCSI drive:

Keeping this in mind, I want to point out the fact that if you decide to purchase an Ultra-160 SCSI adapter (80MB/sec full duplex) and you have a 15,000 RPM drive that can transfer 90MB/sec, you really won't lose more than 5% performance.A SCSI card's interface determines how fast that SCSI controller can transfer data over that connector, meaning that the combined transfer speed of SCSI drives over the cable will not be able to exceed 80MB/sec full duplex if using an Ultra-160 SCSI controller. This is perfectly fine if you only plan on using one drive. However... if you want to run more than one drive or a SCSI RAID setup, you will absolutely need a SCSI-320 controller as you need to be able to support more than just 80MB/sec full duplex on that channel.

Knowing that, we can move on. 

1.  A Drive - You'll need a SCSI drive in the 68-pin format. You can find drives that are either 80-pin or 68-pin. 68-pin drives will have a 68-pin interface for the data cable, a standard 4-pin molex connector (just as on any other drive), and 4 pins for the SCSI ID. The SCSI ID allows you to short out pairs of pins with preset jumpers to assign an ID number to the SCSI drive, similar to how IDE drives need a Master/Slave jumper set. 80-pin drives have only one 80-pin connector and are used for hot swap enclosures. As such, they cannot be used in your computer as they require a SCSI hotswap backpane, which is beyond the scope of this article. Here's a brand new 73GB 15,000 RPM SCSI Ultra-320 drive for $100 shipped (as of 08/14/08), or a nearly new 147GB 15,000 RPM SCSI-320 SCSI Drive for $190 shipped (as of 08/14/08). Last I checked the price of a 147GB 10,000 RPM Raptor X was $180 shipped off newegg, though its currently out of stock. I have no doubt the SCSI drive with NCQ will outperform the Raptor X by a large margin. If you want something comparable to the Raptor X, you can go with these:

Brand new Maxtor 147GB 10,000 RPM SCSI-320 : $100 shipped (as of 08/14/08).

Brand new Fujutsu 147GB 10,000 RPM SCSI-320: $140 shipped (as of 08/14/08).

I've even seen 300GB 10,000 RPM SCSI drives go for less than $1 per gigabyte brand new. Keep in mind, SCSI drives are built to last. These things are designed to handle very high constant loads for 5+ years, and the only one I ever saw fail was is a 9.1GB 10,000RPM drive in a 400MHz Pentium 2 Xeon two years ago. These are rated for a much higher lifetime than 7200 rpm SATA drives are. Also remember that the same manufacturers that make great desktop drives don't have the same reputations in SCSI drives. Maxtor, Fujitsu, and Hitachi make excellent SCSI drives.

2.  A Controller - You'll need a SCSI controller to plug in your SCSI drive. When choosing a controller, keep in mind that the fastest read speed you'll get out of a SCSI drive will be a large 15,000 RPM drive, and will be around 92 MB/sec. Your choice of controller can be either a SCSI-160 non-RAID controller, a SCSI-320 non-RAID controller, or a SCSI-320 RAID controller. a SCSI-160 RAID controller is not advised because it cannot support the throughput of newer 15,000 RPM drives in RAID configurations.

Most of the controllers you can buy at reasonable prices are 64-bit PCI controllers, similar to this Adaptec 39160. I used two of these controllers to run 4 SCSI drives and they were more than capable of meeting the performance needs of those drives. This controller sells for $20 shipped and is more than capable of handling up to 4 SCSI-160 or SCSI-320 drives. Adaptec 39160 on Ebay (as of 08/14/08)

64-bit PCI is different from your standard PCI slot in that it can support a maximum throughput of 266MB/sec. Your standard PCI interface can support a throughput of 133MB/sec, at 32 bits. What you need to know is that 64-bit SCSI controllers *are* backwards compatible with standard PCI slots and will work perfectly fine. If running RAID 0 or RAID 5, however, you will probably want to invest in a PCI-Express SCSI controller.

For single-drive SCSI configurations, your absolute best bet will be an Adaptec 29160N. This card is made for 32-bit PCI slots and has a connector for one 68-pin SCSI cable. Adaptec 29160N + Cable + Terminator on Ebay : $20 shipped (as of 08/14/08). This controller paired with the $100 Maxtor 10,000 RPM SCSI-320 drive listed above would give the same performance as a WD Raptor would at $60 less.

Lastly, you have the option of purchasing a SCSI RAID controller. I personally use an LSI MegaRAID 320-2 in a 32-bit PCI slot and get great performance with two individual drives and one RIAD 1 array. This is a high end controller and comes with up to 128MB of write cache, suppots native NCQ and TCQ, and its extremely powerful. It also comes with a battery in the event that your system's power is interrupted while writing to a drive. The support for Cached I/O *greatly* improves realtime performance in windows. This controller cost me $190 a couple of years back (2006) and was a refurbished model, including a brand new battery. You can find it on ebay now for $185 shipped (as of 08/14/08): LSI MegaRAID 320-2 + battery

However, the PCI slots on standard motherboards don't provide enough bandwidth for RAID 0 or RAID 5 throughput, as those can exceed the 124MB/sec (133MB/sec base2) of a standard 32-bit PCI slot. In those instances, the LSI MegaRAID 320-2E is available for installation in a PCI-Express x8 slot for as low as $190 (as of 08/14/08) shipped here: LSI MegaRaid 320-2E. I haven't listed any PCI-Express SCSI controllers for individual drives, but if necessary I can look some up for you guys. Note that most of the controllers I've suggested here are used off ebay. I have yet to see a *single* broken SCSI controller. These things are enterprise grade and designed to last way past the amount of time any of you use your desktops. This is why I have no reservations suggesting them.

3.  A Cable. Generally these cables run between $10 and $30, and can support between 1 and 7 devices + one terminator. Just remember that it needs to be a 68-pin cable, and that's all you need.

4.  A Terminator. Most SCSI cables come with a terminator included, but if you happen to find a SCSI cable without one, you'll need one. As quoted on howstuffworks.com,

" If the SCSI bus were left open, electrical signals sent down the bus could reflect back and interfere with communication between devices and the SCSI controller. The solution is to terminate the bus, closing each end with a resistor circuit. If the bus supports both internal and external devices, then the last device on each series must be terminated." 

Here's what a SCSI terminator looks like on the back of a cable. You can simplify things by buying a SCSI cable that already comes with a terminator.

If anyone has any other questions regarding SCSI, feel free to ask. 

great article.

If you could just remove the pricing on this, I'll put it as part of the Storage FAQ. Prices change and I'm sure you don't want to check every link for price and update as need be.

Again, great article.

root:

great article.

If you could just remove the pricing on this, I'll put it as part of the Storage FAQ. Prices change and I'm sure you don't want to check every link for price and update as need be.

Again, great article.

Is there another way that I can do that without removing the prices? The prices play a key role in outlining the affordability of a SCSI system, which is contrary to the popular belief that SCSI is very expensive. Can I just put dates next to the prices, such as $100 as of 08/14/08?

Include the dates

root:

Include the dates

 

Done. 

Thanks. Added to FAQ sticky.

Thanks again xtreme. This is a great article i just have a few questions.

on ebay it looks like i can find used 70-80gb 15000rpm scsi drives for around $50. Would i be better off with this drive or a larger 10000rpm drive?
I'm thinking something like this 

I know it's a little much to ask for from enterprise hardware but do they sell nice looking cables like round IDE cables? I haven't been able to find any.

i would like the ability to set up a scsi raid 0 down the road but I'm not sure I can afford to spend that much on a pci express controller. I don't suppose their are any cheap ones. If not I'll probably buy a cheap one and just toss it out if i set up a raid later

Kardon:

Thanks again xtreme. This is a great article i just have a few questions.

on ebay it looks like i can find used 70-80gb 15000rpm scsi drives for around $50. Would i be better off with this drive or a larger 10000rpm drive?
I'm thinking something like this 

I know it's a little much to ask for from enterprise hardware but do they sell nice looking cables like round IDE cables? I haven't been able to find any.

i would like the ability to set up a scsi raid 0 down the road but I'm not sure I can afford to spend that much on a pci express controller. I don't suppose their are any cheap ones. If not I'll probably buy a cheap one and just toss it out if i set up a raid later

To answer your first question, that drive won't work as its an 80-pin drive. 80-pin drives can only be used in hot-swap bays with a SCSI backpane that you typically find only in servers. You will need to find a 68-pin drive, which might be a slight bit more expensive. 

Also, you can definitely find rounded SCSI cables, as I use two of them for my own computer.

Here's a used 4-device SCSI cable with a terminator for $20.45 shipped. 

Used 4-device SCSI cable with Terminator

Just search ebay for "scsi 320 cable" and you should find plenty of them.

Kardon:

ya your right the 68 pin drives did cost a bit more about $20. Would an adapter like this work http://www.1topstore.com/product_info.php?products_id=524? or is that only to go from an 80 pin back plate to a 68 pin drive rather than an 80 pin drive to a 68 pin connector?

Nope, do NOT get an 80-68 pin adapter. They cause interference issues if you ever decide to go with more than one drive, and they also reduce performance, which destroys the point of using SCSI anyway. In some cases I've read of those things reducing performance by as much as 50%.

Trust me, I know 80-pin drives go for dirt cheap, but I made sure not to recommend them for a reason.  I almost bought one when I bought my first 18GB 15,000 RPM drive in 2005 for $150, and even to this day I still think that was worth it. It took me all day to figure out that I needed a 68 pin and not an 80 pin drive. I've done the research for SCSI configurations through and through several times.

So if i understand this correctly, a SCSI 320 non-RAID controller can support 2 individual drives, but if i wanted to run those drives in RAID i would need to invest into a SCSI 320 RAID controller, right?

 Then if that's the case, running them in RAID would take away the price similarity since the difference in controllers is well over $100.  However, it would seem that any gains from running RAID 0 would be insignificant compared to the pure speed of the drives, and RAID 1 can be avoided by establishing a backup drive.

 Am I on the right track on how this works?  Never read anything on SCSI drives prior to this, so its all very new to me.

Drakbak:

So if i understand this correctly, a SCSI 320 non-RAID controller can support 2 individual drives, but if i wanted to run those drives in RAID i would need to invest into a SCSI 320 RAID controller, right?

 Then if that's the case, running them in RAID would take away the price similarity since the difference in controllers is well over $100.  However, it would seem that any gains from running RAID 0 would be insignificant compared to the pure speed of the drives, and RAID 1 can be avoided by establishing a backup drive.

 Am I on the right track on how this works?  Never read anything on SCSI drives prior to this, so its all very new to me.

A non-raid controller can support up to 15 devices per channel. However, it would be unrealistic to try to access any of those 15 at the same time, and the biggest cables you can find are usually 8-device cables.

Also, I'm comparing the cost of individual SCSI drives against 10,000 RPM Raptor drives. You can definitely set up SCSI drives in a software Windows RAID (as you could any type of drive), but it won't be as fast as if it was a hardware RAID. If you ran a proper RAID with SATA drives, you'd still need a RAID controller costing  you upward of $300, because your typical ICHxR chipset will still use your system's memory and CPU to process RAID reads and writes. The only advantage to an ICHxR chipset is that it has a BIOS that manages the RAID array on its own without you having to set one up in Windows. ICHxR motherboards don't have RAID controllers; they have a RAID BIOS that uses system resources. A RAID controller has both a BIOS, its own dedicated cache memory, a processor beefy enough to process the RAID read and write commands, its own independent support for NCQ and other advanced hard drive features, a backup battery unit to finish write requests in the even that your system loses power, and the ability to manage its own command queue very efficiently. 

The gains from running a RAID 0 on a dedicated controller with any type of drive will be much greater than when running a RAID 0 with an onboard RAID BIOS because of the reasons mentioned above. Two 15,000 RPM SCSI drives in a RAID 0, however, will most likely give you more performance than  you really know what to do with, so there's really no point to it. With a 15,000 RPM drive, you have both incredibly fast seek times and incredibly high read and write speeds.

RAID 1 cannot be avoided by establishing a backup drive. Excuse my language, but its a half-assed workaround, since a backup drive will not back up everything in realtime. In the event that one drive fails with a RAID 1, you can continue using your computer until  you get that drive replaced and the RAID rebuilt. If a drive fails with your backup scheme, you not only have no drive to access the data aside from the backup drive, but your backup is only as recent as the last time you backed up the data, which for some people can mean a lot of time and money.

I hope this answers your questions. Let me know if you need me to explain anything further.

XtremeRevolution:

RAID 1 cannot be avoided by establishing a backup drive. Excuse my language, but its a half-assed workaround, since a backup drive will not back up everything in realtime. In the event that one drive fails with a RAID 1, you can continue using your computer until  you get that drive replaced and the RAID rebuilt. If a drive fails with your backup scheme, you not only have no drive to access the data aside from the backup drive, but your backup is only as recent as the last time you backed up the data, which for some people can mean a lot of time and money.

poorly stated but essentially correct.

Drakbak: It is important to understand that the Solution povided by RAID is one of FAIL-OVER, and not DATA SECURITY, which is what backups are for.  Which is why RAID-0 is really....well NOT RAID; it HAS no fail-over.

If your major concern is staying up and running, RAID1 is what you want.  It will NOT however provide DATA SECURITY as BOTH drives are in play at all times. A (admitidly rare,) event like a PSU failing and damaging the mobo and or the HD themselves, or even a controler failure could render the drives un-useable/readable and the data, if recoverable by a 3rd party....very expensive.

Bottom-line, even if you RAID1 you should back-up periodically.

Tallon41

Thanks for the responses, you guys cleared up quite a bit for me.  If I go this route in my next build, I'll probably load my OS and Programs onto a single SCSI drive, then get a regular 7200rpm drive for data storage/etc.   I don't really have anything I'd be worried about losing if a drive were to fail, so I'll just stick to backing up to CDs and such if I have anything  important.  This way I can avoid the RAID configurations and save money by not buying a RAID controller.

 Out of curiousity, how is the noise level of the SCSI's?  I've read that the raptor drives are all very loud with unsettling clicking.  Do the SCSI's offer an improvement in this regard?

Drakbak:

Thanks for the responses, you guys cleared up quite a bit for me.  If I go this route in my next build, I'll probably load my OS and Programs onto a single SCSI drive, then get a regular 7200rpm drive for data storage/etc.   I don't really have anything I'd be worried about losing if a drive were to fail, so I'll just stick to backing up to CDs and such if I have anything  important.  This way I can avoid the RAID configurations and save money by not buying a RAID controller.

 Out of curiousity, how is the noise level of the SCSI's?  I've read that the raptor drives are all very loud with unsettling clicking.  Do the SCSI's offer an improvement in this regard?

Honestly, some are louder than others. They're not particularly silent, but then again they are 10k and 15k rpm drives. My 18.4GB 15,000 RPM drive is pretty quiet though.

Getting a 10,000 or 15,000 RPM drive for Windows and common applications and another 7200 RPM drive for storing data is a very good idea. That's what I started out doing.