IDE, SATA, and SCSI Interfaces

Can somebody explain to me the differences between IDE, SATA, and SCSI?

What are the advantages and disadvantages of each, and what should I know about them, when making a desicion.

SCSI is a standard that allows up to 15 disk drives on a single scsi bus. Most scsi controllers are semi intelligent an that they take care of pumping the data to/from the disk drive without further impact on the processor. Each SCSI drive has a unique ID. Several SCSI drives can talk to the controller at the "same time" by interleaving the data. SCSI devices can talk from one to the other without having to transfer data via the controller (as in disk to disk copy). At one time SCSI was much faster than any of the competitors. Many high end motherboards support booting from a SCSI device.

IDE is a simpler interface where the processor does some or most of the data handling. There can be two drives per bus. Typical current computers have two IDE busses. The newer IDE standard is ATA-133 (?) which is quite fast as long as only one disk needs to talk. All data passes via the IDE controller. Only one disk can talk at a time. Modern ATA devices require less processor overhead than in the past, but still a lot more than SCSI. The fastest SCSI is about as fast as the fastest ATA.

SATA is the newest standard. I don't have the specs and have not really looked into it yet. I hear it's blazingly fast.

SCSI is frequently used in servers because of the lower processor overhead. I've had systems with 140 SCSI drives. Yup, 7 drives per bus. You could not do that with IDE. On the other hand, an 80 gig SCSI 3 drive is about $700, where the IDE equivilent is under $100.

Sometimes with a large data transfer or when you put a CD-ROM in the drive your whole computer freezes for a second or 10. That's the down side of IDE.

Daniel

I have also worked on large systems with one to two hundred SATA disk drives per system (yep--one disk per SATA bus). In this case, they are making controllers with chip sets that support (when I was working on the systems) 6 SATA drives per RAID controller (you had to have separate ribbon cables to each drive).

SCSI Drives have been much more expensive and SATA drives have begun to drive the capacity/performance curves more than the SCSI/Fibre Channel drives.

The downside--SCSI drives have much better error handling and error recovery algorithms than the SATA drives. At the time SATA was still new and they seemed to be working out the bugs in the chips and the interfaces.

I suggest that you look at the RAID controllers--when you start working with such high capacities, it becomes very difficult to make a true tape (or equivalent) backup. You are better off running several drives and using a RAID controller to make sure that you don't lose all of your data in the blink of an eye (I still would recommend that you have separate backups--be they tape or hard disks in a second machine located in another room for any data that you cannot afford to recreate).

I think you will find that SATA disks (whether serial or parallel interface) are so much cheaper than similar SCSI (with their controllers) that you will choose a SATA/RAID Drive/Controller combination with multiple disks for your system. Unless, you are running a mission critical application--then I would look at SCSI or Fibre Channel systems--and be prepared to spend big bucks.

SATA can be made to run more reliably--but it will require time, software, and a lot of testing to equal an off-the-shelf quality SCSI / Fibre Channel system (IMHO based on what I saw a year or so ago).

-Bill

Check out the performance here, pick out your favorite benchmark:

http://storagereview.com/php/benchmark/bench_sort.php

ZD High-End Disk WinMark 99


Rank Drive Name Model Results in MB/Sec
1 Western Digital Caviar WD2500JD 2nd Sample (250 GB SATA) WD2500JD 48.4
2 Maxtor MaXLine III (300 GB SATA) 7B300S0 46.7
3 Maxtor Atlas 15k (73 GB Ultra320 SCSI) 8C073L0 46.5
4 Maxtor MaXLine Plus II (250 GB ATA-133) 7Y250P0 45.0
5 Maxtor DiamondMax Plus 9 [8MB, 80GB/plat] (160 GB ATA-133) 6Y160P0_80 44.9
6 Western Digital Raptor WD740GD (74 GB SATA) WD740GD 44.6
7 Maxtor MaXLine Plus II (250 GB SATA) 7Y250M0 43.2
8 Western Digital Raptor WD740GD 3rd Sample (74 GB SATA) WD740GD 43.1
9 Maxtor DiamondMax Plus 9 [8MB, 68GB/plat] (160 GB ATA-133) 6Y160P0_68 42.4
10 Maxtor DiamondMax Plus 9 [8MB, 60GB/plat] (160 GB ATA-133) 6Y160P0_60 42.3
11 Fujitsu MAS3735 (73 GB Ultra320 SCSI) MAS3735 42.3
12 Seagate Cheetah 15K.3 (73 GB Ultra320 SCSI) ST373453LW 42.0
13 Western Digital Raptor WD360GD (36 GB SATA) WD360GD 41.1
14 Hitachi Deskstar 7K400 (400 GB SATA) HDS724040KLSA80 40.7
15 Hitachi Deskstar 7K250 (250 GB SATA) HDS722525VLSA80 39.8
16 Seagate Barracuda 7200.7 (160 GB SATA) ST3160023AS 39.7
17 Maxtor DiamondMax Plus 9 (200 GB SATA) YAR55VW0 39.7
18 Samsung SpinPoint P80 (160 GB ATA-133) SP1614N 39.6
19 Seagate Barracuda 7200.7 (200 GB SATA) ST3200822AS 39.4
20 IBM Deskstar 180GXP 8 MB (180 GB ATA-100) IC35L180AVV207-1 39.2
21 Western Digital Caviar WD2500JB (250 GB ATA-100) WD2500JB 38.5
22 Maxtor Atlas 10k IV (147 GB Ultra320 SCSI) 8B146L0 38.0
23 Seagate Cheetah X15-36LP (36.7 GB Ultra160/m SCSI) ST336752LW 37.7
24 Western Digital Caviar WD2000JB (200 GB ATA-100) WD2000JB 36.9
25 Western Digital Caviar WD2500JD (250 GB SATA) WD2500JD 36.7
26 Maxtor Atlas 10k III (73 GB Ultra160/m SCSI) KW073L8 36.0
27 Fujitsu MAP3147 (146 GB Ultra320 SCSI) MAP3147 35.6
28 Western Digital Caviar WD800JB (80.0GB ATA-100) WD800JB 35.0
29 Western Digital Caviar WD1200JB (120 GB ATA-100) WD1200JB 34.9
30 Western Digital Caviar WD1000BB-SE (100 GB ATA-100) WD1000BB-SE 33.4
31 Seagate Cheetah 10K.6 (146 GB Ultra320 SCSI) ST3146807LW 33.3
32 Fujitsu MAM3367 (36 GB Ultra160/m SCSI) MAM3367 33.0
33 IBM Deskstar 120GXP (120 GB ATA-100) IC35L120AVVA07 32.6
34 Seagate Barracuda ATA V (120 GB SATA) ST3120023AS 32.2
35 Hitachi Ultrastar 15K73 (74 GB Ultra320 SCSI) HUS157373EL3600 31.6
36 Maxtor DiamondMax Plus 8 (40 GB ATA-133) 6E040L0 30.8
37 IBM Ultrastar 146Z10 (146 GB Ultra320 SCSI) IC35L146UWDY10 30.6
38 Western Digital Caviar WD2000BB (200 GB ATA-100) WD2000BB 30.5
39 Seagate Cheetah 36ES (36 GB Ultra160/m SCSI) ST336706LW 30.2
40 IBM Ultrastar 36Z15 (36.7 GB Ultra160/m SCSI) IC35L036UCPR15-0 30.0
41 Western Digital Caviar WD1200BB (120 GB ATA-100) WD1200BB 29.9
42 Seagate Cheetah 73LP (73.4 GB Ultra160/m SCSI) ST373405LW 29.8
43 Seagate Barracuda ATA V (120 GB ATA-100) ST3120023A 29.4
44 IBM Deskstar 60GXP (60.0 GB ATA-100) IC35L060AVER07 29.1
45 Fujitsu MAN3735 (73 GB Ultra160/m SCSI) MAN3735 28.3
46 Seagate Barracuda 7200.7 (160 GB ATA-100) ST3160021A 28.1
47 Western Digital Caviar WD1000BB (100 GB ATA-100) WD1000BB 28.0
48 Seagate Barracuda ATA IV (80 GB ATA-100) ST380021A 27.5
49 Samsung SpinPoint V80 (160 GB ATA-133) SV1604N 26.9
50 Maxtor DiamondMax Plus D740X (80 GB ATA-133) 6L080J4 26.7
51 Seagate Cheetah 36XL (36.7 GB Ultra 160/m SCSI) ST336705LW 26.6
52 IBM Ultrastar 73LZX (73 GB Ultra160/m SCSI) IC35L073UWD210 26.4
53 Western Digital Caviar WD800AB (80 GB ATA-100) WD800AB 26.1
54 Maxtor DiamondMax 16 (160 GB ATA-133) 4R160L0 26.0
55 Maxtor DiamondMax D540X (160 GB ATA-133) 4G160J8 24.2
56 Quantum Fireball Plus AS (60.0 GB ATA-100) QMP60000AS-A 22.7
57 Quantum Atlas V (36.7 GB Ultra160/m SCSI) QM336700XC-LW 22.1
58 Maxtor DiamondMax 536DX (100 GB ATA-100) 4W100H6 21.9
59 Seagate Barracuda 180 (180 GB Ultra160/m SCSI) ST1181677LWV 21.2
60 Seagate Barracuda 36ES2 (37 GB Ultra160/m SCSI) ST336938LW 20.6
61 Seagate Barracuda 36ES (36 GB Ultra160/m SCSI) ST336737LW 19.4
62 Seagate U6 (80 GB ATA-100) ST380020A 17.4
63 Samsung SpinPoint P20 (40.0 GB ATA-100) SP4004H 17.2
64 Samsung SpinPoint V30 (60.0 GB ATA-100) SV6004H 14.9
65 Samsung SpinPoint P40 (80 GB ATA-100) SP8004 12.8





A good read:

http://www.storagereview.com/articles/200406/20040625TCQ_1.html

An interesting article on SATA and RAID 5:

http://www.tomshardware.com/storage/20040625/index.html

I take it those are sequencial read/write ratings. How relevent is the random access time?

If you are after raw read/write/access speed... You are much better off looking into RAID based controllers with multiple disk drives operating in parallel.

The high-end disk drives are all pretty similar to each other. You should easily be able to obtain 2-4x the read/write performance with 2-5 drives using RAID.

The controller vendors where selling bunches of 2 port SATA controllers to gamers who wanted to speed-up their systems.

Again, you also need to ask how important is your data to you. If you simply strip your data across the drives for speed (no ECC across disks), you will increase throughput--2 disks is twice as fast, 5 disks are five times faster. However, your reliability (chances of loss of data) also go up by 2-5 times. If you setup 5 drives, 4 for data and one for ECC, you will increase data throughput by four times, and your data should be, roughly twice as reliable as one drive (assuming you replace a bad disk as soon as it fails).

-Bill

Interesting - will have a closer look at those links later especially if you can run a benchmark test! I'm using 2 SATA Western Digital 10k 36GB Raptors at the mo in Raid array O (striping) config, installing software is superfast, I can install Win XP in 5mins 47secs!!!

IlluminatingBikr,

Did the PM I sent a few days ago get to you?

Sub

i like sata cause its such a small cable.i hate clutered pc cases

IDE standard and SATA are different flavors of ATA. You'll commonly see IDE drives referred to a PATA (Parallel ATA).

I hear there are still a few bugs to be worked out of SATA - there are some slight incompatibilities between different vendors' implementations of the protocol, there's some skullduggery going on with secret committees setting the spec, and the data cables are rather sensitive to interference.

I'm not sure that SATA data transfer speeds are that much faster than PATA - I've heard that 150 MB/s is tops for current-generation SATA. PATA is going at 133 MB/s right now. You're never going to get anywhere near either of those numbers in the real world.

SCSI drives are typically more mechanically reliable than ATA drives since they're targeted at the server market. They're designed to run 24/7 for years on end with stretchecs of intense usage.

SCSI also has other advantages. You can hot plug a SCSI 2 or newer drive. Yup. Pull it out off of the bus while data is being read/written to the other drives on the same bus.

I've upgraded a 250 gigabyte SCSI array to a 750 gig array without stopping the database or rebooting anything. Even the box holding the drives was swapped out.

Daniel

That must have taken a bit of time while each drive syched itself with the array.

IlluminatingBikr, you have not posted your use for the drive(s). bottom line is most folks will not spend the extra $$$ for SCSI unless they are setting up a server. Most folks at home will not set up RAID controllers.

Myself I'm running multiple drives, using SCSI drives for applications that need faster access. Then running some EDE drives for bulk storage.

IDE RAID 5/10 is getting affordable and cheap for the home power-user/enthusiast with hundreds of gigabytes of files.

Sorry guys, I just got home from work, and had a friend over before then, who spent the night, so I have been away for a while. Glad to see I have been miseed. /ubbthreads/images/graemlins/smile.gif Lol.

Sub_umbra-
Yes, I did get your PM. I appreciate your advice. I apologize for not letting you know this sooner.

cy-
Originally I was just curious and on a knowledge quest, so I didn't think my personal need would be relavent.

I am actually just looking for the best setup for a personal computer. I will most likely be using just one hard drive, and would like the option of expanding to two. I guess I should probably just stick with regular IDE? I don't need error checking, or 100 hard drives. /ubbthreads/images/graemlins/blush.gif

[ QUOTE ]
idleprocess said:
That must have taken a bit of time while each drive syched itself with the array.

[/ QUOTE ]

It didn't take that long. I recall we finished the process in 1 day. The arrays were set up so that each SCSI Bus (channel) was configured with one less drive than would be needed to flood the bus. That allowed each drive to simultaneously run at it's maximum speed. The logical drives were mostly raid 0+1 (striped and mirrored) with the mirror in a seperate enclosure so the syncing of the drives was rather quick.

Much of the time was spent ensuring that we knew where each slice was. There's nothing quite as sickening as realizing you've just pulled out the disk that provides the redundancy for the disk in your other hand.

That is the other problem with raid 5. If you have 6 disks (5 data and 1 parity) and you lose one, you are OK. If you lose two, you are dead in the water. With mirroring, if you lose two you are OK as long as teh second does not have the same data as the first one you lost. I bring this up becasue many people use raid-5 instead of backups.

Realistically, most folks do just fine with ATA-133 and one disk. Most folks rebuild their machien when it crashes anyway. /ubbthreads/images/graemlins/smile.gif (not I, BTW)


Daniel

I use serial ATA if the motherboard supports it, just because it's the wave of the future. They work just like the old fashioned kind as far as I can tell.

The cables are smaller. In the future they will be capable of higher speeds.

RAID 5 is no excuse not to backup data. It is the most efficient way to provide fault-tolerance, which is why it's so popular. You still need a well-considered offsite backup plan.

I'm just suggesting that one be careful with SATA. It uses serial transmission, so it has to operate at substantially higher bitrates than PATA - making it more susceptible to interference.

About a year or so ago, I was testing SATA (then new) and found that it seemed to be pretty reliable electrically... The only problem at the time was the SATA cable connectors were pretty flimsy and broke easily. The cables were stiff but mini-coaxial (as I recall) and should be pretty a good signal environment wrt interference. And SATA is a differential interface--not ground referenced like IDE/PATA--which usually improves overall signal integrity.

We had more problems with the IDE/PATA ribbon cables/connectors being miss-handled. We had broken connector pins, cables torn from connectors at sides of cables, and punch trough by sharp component tails and sheet metal. Depending on what signal(s) was shorted/open/grounded--we got some pretty weird errors.

I would not really worry about SATA signal quality from what I had seen.

-Bill

I used SCSI for many many years with great success. As was already mentioned, these days these are mostly server drives. The good ones are expensive but they are tanks and will run forever. A lot of Mac users discovered that cheap ATA drives aren't of the same quality as the SCSI disks they were used to after Apple switched from SCSI to ATA as the internal buss however many years ago. But at least I could afford to buy more disks even if they didn't last as long /ubbthreads/images/graemlins/smile.gif

I've got good feelings about SATA though. Idleprocess is right to be suspicious of new interconnect specs. There will undoubtedly be low level driver and card issues as it gets itself totally flushed out. The serial spec though I think is very well done and at least as resistant to any problems as ATA is. I worked with some folks doing some stress testing of it recently and they found nothing, nada, no problems at all that they were able to create. Their conclusion was also that it was less CPU intensive than regular ATA is. I don't know if thats really true, but it was their impression.

The old story was that SCSI was fast but expensive because all the drive handling was done by the SCSI controller. The CPU just handed off data to be written or asked for data to be read and waited for it. ATA is cheap because the controller circuitry is much simpler and requires a lot of software in the CPU to control and manage it. The massive improvements in CPU performance have made ATA drives comparable in performance to SCSI, but it is at a cost in performance in the rest of the machine. Their impression was that SATA was requiring less again, which would be good, let us get a little bit more performance out of our already overheated CPU's /ubbthreads/images/graemlins/wink.gif but again, I don't know if thats really true or not.