USBvsFWvsSATA Ext. Drives - The Comprehensive(?) Guide!

Question

Maybe not the most comprehensive, but I see this topic come up over and over again. Hopefully this will answer pretty much everyone's questions. AFAIK everything here is pretty accurate, but I'm not perfect, so do your own research!
OK, before we begin, you must understand that the fastest any drive will work will be the slowest spot in the chain (generally the platters, or the physical interface). If you put a SATAII drive in a USB 1.1 enclosure, not only will the drive simply crawl, but you have wasted a great deal of money! So, let's look at the specs of interfaces, then the drives, and then put it all together.
These numbers are averages, and sometimes educated guesses. So not all here is set in stone. A lot of the numbers are gleaned from www.storagereview.com - a great site for drive benchmarking, etc.
First we need to understand the difference between burst speed and sustained throughput. Burst is just what it sounds like. Just a quick burst of data. Sustained throughput is what really matters in drives. This is actually how fast data can move to and from the drive continuously. Streaming video, copying of large files, etc. all rely on *sustained throughput*. This is the benchmark that matters, not burst.
Most drive speeds are shown as the actual interface speed (the speed with which data can be moved from the controller & cache to the interface on the PC). This speed is fast because it is all electronic transfer. However, the actual drive speed is slower because the platters, etc. all have moving parts, and are slower than the interface speed. Also, this "extrenal transfer rate" has almost NOTHING to do with the capabilities of the drive itself. It is simply the FASTEST link in the chain (pure electronic transfer), & therefore what the marketing folks like to use. The drives internal characteristics are what limits its performance.
Disk Platters --(STR)--> Cache --(ETR)--> IDE interface on your PC mobo.
Lets look at the external transfer rates (ETR) compared to the real world sustained throughput (STR) rates:
- USB 1.1 - so slow, don't even think about it.
- USB 2.0 - 480Mbps = 52MBps. This is BURST ETR. Sustained Throughput is MUCH slower. According to Storage Review once you take away the overhead of converting data from IDE or SATA to USB, the USB protocol, etc. USB gives you an effective sustained throughput of around 26MBps, or 208mbps. A far cry from 480 burst that USB 2.0 claims. And that is the maximum. Now you need to find a drive that performs as close to that maximum as possible...
- FW400 - 400mbps = 50MBps - this speed, however, is sustained throughput. IOW, even though the numbers are smaller than USB 2.0 (400 vs 480) a FW400 drive is going to be a lot faster. How much faster? Well, not as much as you'd expect. IIRC the actual sustained throughput of a FW400 drive (remember there is overhead) is in the neighborhood of 35MBps, not 50MBps. THis is the speed of actual data streaming from the drive to the PC/laptop, after overhead. 35+MBps.
- FW800 - 800mbps - 100MBps - I don't have any actual numbers for this. If FW400 is doing 35MBps, then I would guess that FW800 is somewhere between 70MBps & 80MBps (if your drive is fast enough to pump data out that quickly!). FW800 would be a little more than twice FW400 (well, theoretically at least) because you only have to subtract the overhead once, not twice. Now, IDE drives, no matter what the interface, are not going to give you sustained throughput this fast, but it does have advantages as we will see with SATA over FW400.
-eSATA - 1.5Gbps = 187.5MBps - In the real world, SATA drives (15k and 10krpm ones no less) will give you somewhere close to 80-90MBps sustained throughput. Not the 187 theoretical limit.
- IDE/ATA/33 = 33MBps or 264mbps - In the real world, sustained throughput from these drives is going to run around the 23-26MBps mark.
- IDE/ATA/66 = 66MBps or 528mbps - In the real world there is almost NO difference in speeds between ATA33 and ATA66 drives. Many times a 7200rpm ATA33 drive can outperform a 5400rpm ATA66 drive. Often times when you see benchmarks showing much better ATA66 performance over ATA33 performance the reason is that the ATA33 drive is a 5400rpm drive, and the ATA66 drive is a 7200rpm drive!
- IDE/ATA/100/133 - There is very little throughput advantage to these either. They do come in faster rpms. In fact the difference is so negligible, that at one point IBM called their ATA100 drives "ATA66+"
SO then, what is the point of ATA100 over ATA33 then? Well if the data that you need is *already in the cache* of your drive, then it will move from the cache to your PC mobo at the ETR speed of 100MBps (in the case of ATA100). This situation is such a small percentage of the requests for data made to a disk, that when you average it out, the results are negligible.
All of this being said, at times it can be a waste to put an ATA100 drive into an ATA33 mobo. For one thing, ATA100 drives are more expensive. For another thing, on those rare occassions where the data you want IS in the drives cache, it can't move it to the PC at 100MBps, it can only do 33MBps.
So, what makes a drive faster? The bottleneck is getting data from the platters to the cache. So, a faster rotational speed will get the data there faster. If you have a 5400rpm ata33 drive, lets say it's getting data to the cache at 20MBps. Now get a 7200rpm version of the same drive, and you may get data at an STR of 26MBps. Both drives are ATA33, and both drives are identical sizes. That 7200rpm ata33 drive can easily be faster than a 5400rpm ata100 disk. Of course different drives have different performance specs... Not all 100GB 5400rpm drives are alike, as we will see at the very end of this post!
OK, so a summary at this point:
Interfaces
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USB 2.0 = ~26MBps (real world STR)
FW400 = ~35MBps
FW800 = ~80MBps (educated guess)
eSATA = somewhere in the 100MBps I would guess I have not seen any SATA interface benchmarks, though I have seen SATA drive benchmarks
Drive Interfaces
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NOTE: with drives there is a range. The higher speeds in the range are generally the 15krpm and the 10krpm drives, at least in my SATA numbers.
ATA33 = 23-26MBps
ATA66 = 23-26MBps
ATA100 & 133 = 23-26MBps
SATA = ~70-90+MBps
So, what drive and what interface to get? USB? FW400? Expresscard-FW800? Expresscard-eSATA? Well, it depends on what you wanna do, really. For streaming video editing, you need 3.6MBps per stream. Remember there will be additional overhead (possibly) on the drive. If you are streaming 2 video streams, each with 2 audio tracks, the drive has got to look that stuff up and stream it from the drive to your application. Hopefully you have a lot of RAM!
Remember that a 5400rpm desktop drive will be slower than a 5400rpm 2.5 laptop drive because the laptop drive is smaller so the same rpms with less physical space to search means faster access times. ALso remember that a 250Gig desktop drive will be slower than an 80Gig laptop drive. Smaller capacity drives are faster which is why you don't see real data warehouse raid servers running multiple 500Gig drives, but rather multiple 120Gig drives. So a 100Gig 7200rpm IDE drive can easily (again depending on the particular drive) smoke a 300Gig 5400rpm desktop drive, and even it's 7200rpm equivalent.
SO (by interface):
If your external hard drive is going to connect via USB (~26MBps) then you want a drive that can take full advantage of that. If you are just transferring data for backups, or copying files back & forth, then any old IDE drive will be just fine. If you are doing video and want to maximize your performance, you want to use as much of that 26MBps bandwidth as possible. Get a 7200rpm IDE drive. A 5400rpm may suffice (again not all 5400rpm drives are equal as I will point out shortly). SO how fast is a 7200rpm drive via USB going to be as compared to a desktop drive? It will be at least on par with any 5400rpm desktop drive, and possibly on par with many 7200rpm desktop drives. See becnhmarks taken from storagereview.com at the end of this post for a limited laptop<->desktop comparison.
Now, if you want to connect via FW400, you want to maximize that 35+MBps bandwidth, right? What are your options? a 7200rpm IDE drive, or a 5400rpmSATA drive (a 7200rpmSATA drive for FW400 is a complete waste of money at this point). So you can get 26MBps from the 7200rpm IDE (wasting only about 9MBps), or MUCH higher from the SATA. The problem is that even if you are getting say 70MBps from a 2.5" external SATA drive (which would likely have to be a 7200rpm drive), you are still limited by the 35+MBps speed of the FW400 connection. You can spend a lot more money and max out that 35MBps w/ SATA, or get slightly lower performance with a 7200rpm IDE drive. THese days, the SATAs are as cheap and in some cases cheaper than the equivalent sized 7200 IDE drives. However, there are caveats (see below) that may make you think twice about getting that SATA over the 7200rpm IDE! Oh, and 7200rpm IDEs are getting faster STRs all the time.
FW800. Basically the same arguements as with FW400. Here's the thing.... why get the FW800 expresscard unless it's REALLY cheap? For about the same price you can get an eSATA expresscard and get better performance (how much is up for debate). Personally I would not even think about FW800. It would be either USB/FW400 on the lower-end, or eSATA on the higher end. FW800 for IDE drives is a waste. Use the internal FW400 port if you can.
eSATA - well, you have no choice. You HAVE to get a SATA hard drive. SImple!
CAVEATS:
Here's the thing. WIth 2.5" drives, IDE drive can operate off of USB bus power. SATA drives often need an external power source. The USB spec only outputs up to 500 or 600 milliamps of power via USB. This is fine for many SATA drives when it comes to reads & writes. However, many require more power for spinup. The Hitachi low power 5k100 SATA drive requires up to 1 amp (1000 milliamps) of power at spinup. The hitachi rep told me that his drive may work on USB power, but running the drive through it's paces would likely need an external (plug into the wall) power source. This is a low power SATA drive too.
Now, if you are going to plug into the wall ANYWAY, then why not just go ahead and get a 3.5" enclosure? For the same price of a 100GB 2.5" SATA drive, you can get a 300GB 3.5" SATA drive! The 3.5" SATA enclosures are a lot cheaper than the 2.5 ones as well.
IDE drives require less power than SATA and can be powered off of the USB port (2.5" drives only - all desktop drives will require AC power!)
CAVEAT #2:
Do you plan to boot windows off of this drive (using the BootCamp windows install hack that allows you to have a small 5Gig windows partition on your Mac for bootstrapping Windows, and where the rest of the windows files are installed to the external drive)? If this is your goal, then Firewire is NOT an option for you!. Windows will NOT boot off of a firewire drive. It will boot off of a USB drive (with the aforementioned hack), or eSATA (w/o the hack).
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CONCLUSION
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So, I think the best options boil down to the degree of freedom and mobility that you want. If you want a truly portable drive that is not tethered to a wall outlet, then you MUST use an IDE drive, and not SATA. Given the 26MBps real world STR of IDE, and the similar max STR of USB 2.0, this combo makes the most sense. IF you are using your USB ports for other stuff, you can get a FW400 enclosure, or a USB/FW enclosure. FW/USB combo enclosures run around 50% more in price than USB 2.0 only enclosures (iow, about $10 more). And there is not much use in using FW400 unless you have a 7200rpm IDE drive, AND you can't boot from a FW drive if you wanted that option.
If you don't mind being tethered to a wall, I think the best solution for the money is to get a 3.5" SATA enclosure so you can get a much larger drive for your money. It's your choice whether you want to buy a FW800 or eSATA expresscard (I would pick eSATA - no SATA to FW conversion overhead). If you don't want to spend the $100 or whatever on an expresscard, get an external SATA enclosure that is both SATA to eSATA and SATA to FireWire. Again, booting off of Firewire is not an option (at least not for Windows).
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P.S.
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One last point: Not all drives are alike!
Quick and simple point... 2 virtually identical 2.5" 7200rpm drives from different manufacturers can perform very differently.
Take a look at the SR High-end DriveMark2006 scores for the following drives (Higher is better):
Hitachi Travelstar 7k100 (100GB, 2.5", 7200rpm, IDE) = 413
Seagate Momentus 7200.1 (100GB, 2.5", 7200rpm, IDE) = 366
Seagate Momentus 5400.2 (100GB, 2.5", 5400rpm, IDE) = 332
Hitachi Travelstar 5k100 (100GB, 2.5", 5400rpm, IDE) = 326
Western Digital Scorpio WD800VE (80GB, 2.5", 5400rpm, IDE) = 287
What this means is that the Seagate 5400rpm is almost as fast as the Seagate 7200rpm drive, with the Hitachi 5k100 neck & neck! The WD 5400rpm drive, however, is noticably slower.
How does this compare to other drives?
The same test performed on high-end desktop drives (these were the ones that scored the lowest - there were some amazingly fast drives - they are also expensive drives)
Seagate Cheetah 10k.7 Desktop Mode (300GB, 3.5", 10000rpm, Ultra320 SCSI) = 412 (that is SLOWER than the Hitachi travelstar 7k100 IDE drive!!!)
Seagate Cheetah 10k.7 Server Mode (300GB, 3.5", 10000rpm, Ultra320 SCSI) = 410
Hitachi Deskstar 7k400 w/ TCQ (400Gb, 3.5", 7200rpm, SATA) = 392 (Hitachi's own notebook drive beats the SATA in these benchmarks!)
Seagate Savvio 10k.1 Server Mode (74GB, 3.5", Ultra320 SCSI) = 375
Hitachi Ultrastar 10k300 (300GB, 3.5", Ultra320 SCSI) = 369
(look at www.storagereview.com for the bench marks and an explanation of this particular benchmark.)
This means that those IDE notebook drives are pretty fast drives, and can even keep up with some SATA and Ultra320 SCSI desktop/server drives! Unfortunately I could not find STR numbers for the laptop drives on storagereview.com or any other location. If anyone knows of another site, I would love to see the results.
-Brain21
MacBook Pro   Mac OS X (10.4.7)  

Answer 1

So, which FW400 portable drive (brand & model) would
you personally recommend?
Regards,
Neither!
Actually, I am going to be booting Windows from a 5Gig internal (bootcamp) partition and the OS files will reside on the external drive. This limits me to SATA & USB.
I am going to get a USB 2.0 enclosure and get one of those 4 drives mentioned at the end of the article (Hitachi TravelStar 5k100 & 7k100 & the Seagate Momentus 5400 and/or 7200rpm drives). That will be my "mobile" solution.
Then, I'm going to find a SATA enclosure (3.5") that does eSATA and FW. I'll clone my mobile drive onto that (well, at least the windows install). I'll run FW400 until prices for the eSATA cards come down to the $50 range (the cards are already there - well one brand is, but there are no mac drivers for it, just windows... so maybe that cheap one will work for me...)
Don't know what brand & size 3.5 drive I'm gonna get.
As for the enclosures, there is something that I don't know that much about. How much of a difference do the chipsets on these things really make a difference? Oxford is the only chipset that I know by name, but I am going to stay away from those. I saw a recording studio lose thousands of dollars worth of recorded time (that they had to refund) because the oxford chipset on their external HDD died and took the drive with it. When I took it to a data recovery specialist friend of mine and told him what happened his first question was "Oxford chipset?" I'm sure that they are much improved now over 2 years ago, but I don't want to take any chances.
Brain21