SCSI Card

SCSI Card

Description
Notes on SCSI and IDE RAID
What To Look For
Recommendations

Already know what a SCSI Card is and what to look for? Then skip to the Recommendations.

Description:

A SCSI card is a card that will control the interface between SCSI versions of hard drives, CD-ROM drives, CD-ROM burners, removable drives, external devices such as scanners, and any other SCSI components. Most fit in a PCI slot and there is a wide range of types. The three main types of connectors on these cards are 25-pin for SCSI-1, 50-pin for Narrow SCSI, and 68-pin for Wide SCSI (and Ultra-Wide SCSI, Ultra2-SCSI, Ultra160 SCSI, and Ultra 320 SCSI - all of which use a 68 pin connector).

SCSI controllers provide fast access to very fast SCSI hard drives. They can be much faster than the IDE controllers that are already integrated your computer's motherboard. SCSI controllers have their own advanced processing chips, which allows them to rely less on the CPU for handling instructions than IDE controllers do.

For the common user, SCSI controllers are overkill, but for high end servers and/or the performance freaks of the world, SCSI is the way to go. SCSI controllers are also much more expensive than the free IDE controller already included on your motherboard. There is also a large premium in price for the SCSI hard drives themselves. Unless you have deep pockets, there isn't much of a point in going with a SCSI controller.

Many people buy SCSI controllers just for use with their CD-ROM burners and CD-ROM drives (these drives must be SCSI drives of course).

SCSI cards also have the ability to have up 15 devices or more per card, while a single IDE controller is limited to only 4 devices (some motherboards now come with more than one IDE controller though). SCSI cards allow these drives to be in a chain along the cable. Each drive on the cable has to have a separate SCSI ID (this can be set by jumpers on the drive). The last drive on the end of the cable (or the cable itself) has to "terminate" the chain (you turn termination on by setting a termination jumper on the drive - or use a cable that has a terminator at the end of it).

Notes on SCSI and IDE RAID:

RAID stands for Redundant Array of Independent Disks. RAID arrays combine multiple hard drives to act as one. You have to have at least two drives for a RAID array, and in some cases you need more. RAID is generally considered overkill for home users, although it is very important in the server market. For those really interested in high peformance, a RAID array may be worth setting up. The primary benefits of RAID include Redundancy and Performance, although not always both together. There are several different levels, or types, of RAID arrays. I'll discuss the four primary forms, their benefits, and their disadvantages:

1. RAID 0 is first, and it is also known as a Striped Array. In this level with 2 drives, part of the data is stored on one drive, and part of the data is stored on the other. This way, the RAID card can write a small amount of data to both drives at the same time about twice as fast as a single drive could write the same amount of data. The RAID card can also read data from the two drives at once, making read speeds twice as fast. This RAID setup is all about performance and does not provide any redundancy. If one drive dies, all data is lost. RAID 0 is good for desktop situations where data is not mission critical, but it is a good idea to make backups often. Since data is not reproduced, two 36 GB drives would be seen as one 72 GB drive.
2. RAID 1, which is also called Mirroring, uses 2 drives and has the exact same data on each drive. The major advantage of RAID 1 is redundancy. If one drive dies, the computer can keep going normally. Read speeds are also sped up because the drive can read different parts of the data from each of the two drives at the same time. Write speeds are slower than a single drive though because the RAID card has to write the same data to both drives instead of just writing once to one drive (or across multiple drives like in RAID 0). RAID 1 can be good for keeping backups of your important data, while also increasing read speeds. It can also be helpful in web servers, since reading is what is done most often. Since data is reproduced, two 9 GB drives would be seen as one 9 GB drive, so you don't get the full benefit of all drives.
3. RAID 5 is Striping with Distributed Parity. This configuration requires at least 3 drives. It provides the same performance as RAID 0, and also adds the redundancy of parity. A "parity bit" of the data is distributed across all the drives so that if one drives dies, the array can continue working okay, but you would need to replace the third drive. The calculations can slow write speeds though. This also gets expensive since 3 drives are required. RAID 5 is most commonly used in big enterprise servers. Most IDE RAID controllers do not support RAID 5.
4. RAID 0,1 is also worth mentioning. It combines RAID 0 and 1 to stripe two drives, and then mirror those two drives on another two drives. Thus, a minimum of 4 drives is required. You get speed improvements, but also keep redundancy. The server you're viewing this web page on actually runs a RAID 01 array!
5. RAID 1.5 is a new RAID format that combines mirroring and striping with just two drives (which should provide good reliability and speed). The jury's still out on how well this works. I don't know much about this new format yet.

What To Look For:

• The type of controller is the most important thing to consider. If you want a controller for hard drives, you might as well get the Ultra320 controller since there isn't much of a price difference (if you find one significantly cheaper that's Ultra160, it should be sufficient). If you want to get a controller only for CD-ROM / CD-RW drives, then narrow SCSI (50 pin internal connector) is all that is needed.
• Transfer rate is another thing to consider. These are usually determined by the type of SCSI card, which can be SCSI-1 (10 MB/sec Max), Narrow SCSI (20 MB/sec Max), Wide SCSI (40 MB/sec Max), Ultra2Wide SCSI (80 MB/sec Max), Ultra160 SCSI (up to 160 MB/sec Max), and now Ultra320 SCSI (up to 320 MB/sec Max). Before you jump to conclusions and determine that Ultra320 is a must have since it is "twice as fast" as Ultra160, be warned that the two controllers will yield no speed difference when only 1 hard drive is connected. You might not even notice the difference with 4 hard drives connected. 320 MB/sec Max simply means that all drives on the card can transfer a total of up to 320 MB per second. Since 1 drive will not currently transfer data nearly that fast, it's pointless for a single drive. However, if you have 10 drives in a heavily accessed server, the 40 MB/sec limit of Wide SCSI may actually slow things down.
• Number and type of connectors are obviously important. If you get a 68-pin Ultra320 drive, you want to have a 68-pin Ultra320 connector on the SCSI Card (although a 68-pin Ultra160 connector would be sufficient - even a 68-pin Ultra2Wide or Ultra2 connector would work if you have something to terminate the chain). If you've got an external Narrow device, then you need a 50-pin connector on the external portion of the card (this may be used for scanners or external CD burners). However, there are adapters to get around these problems, but they are not always 100% effective (not to mention that you lose out if the device is (for example) a 50-pin device and you try to connect it to a 25-pin port).
  If you are looking for a SCSI controller that will do it all, you want to have an internal 68 pin connector (preferably Ultra320) for hard drives, an internal 50 pin connector for CD drives, and an external 50 pin connector for scanners and other devices (or external 68 pin connector for additional hard drives).
• The Chipset on the SCSI card is also important, but I don't know a lot about the chipsets. I DO know enough to say that the Tekram and Symbios Logic chipsets are good (and can be found quite cheap) and Adaptec's chipsets are considered to be the best.
• Some motherboards have SCSI controllers on them. If you're getting a whole new machine, this may be the way to go if you want SCSI. The motherboards are more expensive, but it is less expensive than buying a SCSI card. The only problem is that if you decide to get a new motherboard later on, you can't take your SCSI controller with you, but you could if it were a separate controller... Thus, you will spend more in the long run if you plan to upgrade your computer like that.
• If the SCSI controller is going to be used for a large number of hard drives, getting a dual channel card may be helpful. This can provide a speed increase in addition to supporting more devices. Have a dual channel SCSI card is kind of like having 2 SCSI controllers in one computer (2 of each connector usually).
• If you're getting a RAID controller, be sure it supports the RAID levels you need. RAID 0, 1, 5, and 0/1 are the most commone levels that you would want supported on your RAID card.

Recommendations:

SCSI Controllers

SCSI RAID Controllers

IDE RAID Controllers

• SCSI Controllers:
• Before I get to my recommendations, I want to note that they are mainly for using SCSI hard drives or a combination of hard drives and CD drives. If you *only* want a SCSI card for use with CD drives and other 50 pin internal devices, or for external 25 pin devices, then I would suggest Adaptec's 2906 which has a 50 pin internal connector and a 25 pin external. Although it's no longer being made, the Adaptec 2903 or 2903B is about the same controller, and you may be able to find it for a lot less!
• My number one pick in all around SCSI controllers is the Adaptec 29160N. Combining the speed and reliability of Adaptec leaves you with an exceptional SCSI controller. All of the Ultra160 controllers from Adaptec are excellent, but this one is the best card to get for general use because of the connector options it has. Of course, this mostly depends on your situation. The 29160N has an internal 68 pin Ultra160 connector as well as a 50 pin internal connector for CD drives. The 50 pin external connector is handy for connecting SCSI scanners and other external devices. This card is also very cheap now.
  The cheaper 19160 has most of the features of the 29160N, but it is only supported under the Windows operating systems.
  Adaptec's other Ultra160 controllers all have 68 pin Ultra160 as their external connections, so they aren't good to have unless you wish to connect external hard drives.
• The Adaptec 29320-R is a good choice for an Ultra320 SCSI card. It has one internal and one external 68 pin connector as well as a 50 pin connector for legacy devices. If you don't need the 50 pin connector, the 39320-R may be a better choice.
• Adaptec's older model, the 2940U2W is also a great controller, but since the 29160N is about the same price, I'd advise getting it instead.
• Tekram also makes some good controllers. If price is a concern, go with a Tekram card.

• SCSI RAID Controllers:
• I don't have much current experience in this area anymore, although I would expect Adaptec's products to be a good option.

• IDE RAID Controllers:
• I don't have much current experience in this area either, but I would suggest looking at Promise and Abit controllers as they have been good brands in the past.