Noob question 'bout SCSI

[wizdum]

I understand the following interfaces: IDE, SATA, & RAID. One thing that I have sort of neglected throughout my computer geek career is SCSI. What is it? I know the basics. It's a storage interface, and it's fast. Will anyone else give me some info on it or hook me up with a link? I've already searched the AT FAQs. Thanks alot.

-Groov

 

[Matthias99]

I understand the following interfaces: IDE, SATA, & RAID.

Um... I have to question your understanding a bit here, since 'RAID' is not an 'interface' like [E-]IDE, SCSI, and SATA are.

SCSI, the Small Computer Systems Interface, is another way to connect I/O devices to a computer. It is an older standard than IDE -- I believe it's been around since the 1970s. It was designed to be more flexible and expandable, and also to run at higher speeds.\

Advantages of SCSI include the ability to attach large numbers of devices (up to 16 on a single chain), and with support for up bandwidth of up to 320MB/s (IDE is limited to 133MB/s and two devices per cable). SCSI chaining allows you to connect multiple devices one after another, and allows the use of external disk arrays without any extra effort. Most high-end RAID controllers, etc. are built for SCSI, as it is generally used in large-scale servers and disk storage arrays. 15kRPM drives are currently only available in SCSI.

Disadvantages include more expensive controllers and drive interface hardware, and having to muck with things like device chain termination (it's much tougher to configure than IDE). Thus, it is rarely used for low-end desktop PCs. Also, 133MB/sec. (the current speed limit for IDE) is WAY more than any current single disk drive can supply; SCSI offers little performance benefit nowadays unless you need many drives or are using a RAID array. It's been steadily losing market share in low-end servers and workstations to IDE and SATA over the last few years, and SAS (Serially Attached SCSI, basically SCSI over SATA) may finally kill off native SCSI controllers and drives in the near future.

 

[ragiepew]

Where to begin... You're right, SCSI (Small Computer Storage Interface is what I believe it stands for) is storage interface, much the same as IDE and SATA (not RAID though). Without getting into the very technical differences, its just another stage interface and as such requires three things to run on a common computer.

1. SCSI interface card. You can add in a PCI card and/or some motherboards have SCSI interfaces built in (usually higher end workstation/server boards for example)

2. SCSI cable. This is obvious but a specific cable is necessary.

3. SCSI HDD. The actual harddrive must have a SCSI interface.

Now, Phisically/Technically, there is no difference between SCSI hard drives and IDE/SATA... they are all the same. The only difference is in the interface. So, in saying that SCSI hard drives are faster, this is actually not becaue they are SCSI but more because SCSI is usually used in high-performance conditions and most SCSI hard drives are geared towards that. Also, people who buy SCSI (corp. america) is use to spending large (relative) amounts of money on storage and new (read: fast) technology is always more exensve... again, leading to SCSI drives being faster.

There are many levels of SCSI (U160/U320 for example)... think of them as versions of ATA (66/100/133) in that each supports a higher amount of theoretical throughput. Also, SCSI can support 15 devices per channel unlike IDE (and even SATA which is point to point single device).

Anyway, this is just a rough explanation... if I've missed something I'm sure someone else will add.

 

[ragiepew]

looks like I got beat by a few seconds...

 

[Markfw]

Also in addition to what has been said here, RAID can be used on IDE, SATA or SCSI. Since SCSI can have so many devices attached (read drives), in a SCSI raid array, you can get much bigger total single drive size (read logical) or much faster due to many more heads seeking.

Also, technically they are vastly different, much more complex than IDE or SATA ($$$).

 

[Zepper]

Lots of good SCSI info: http://www.scsifaq.org
Good SCSI vendors:
hypermicro.com (may offer free ground shipping if you mention www.storagereview.com - check the SR site for the latest offer)
centrix-intl.com
pc-pitstop.com (offers PayPal as a payment option)
scsi4me.com (ditto)
and I can usually find stuff for low bucks on eBay.

.bh.