Switching harddrives


I'm currently teaching three cources at a school in my area. All classes share the same computer, and in the past the have seperated the different classes with different partitions in the harddrive.

I would like to install three seperate drives in the computer, set them all to master and connect the to the same IDE controller. Between the IDE controler and the harddrives, I would like to place a switch that make's it possible to select what drives is going to be active. I remember that

I have seen setups like this in the paste, and by this way every student get there own harddrive, and it will be almost impossibel to mess up for another student, by erasing the boot sector or something like that.

And now on to the question. What pins must I disconnect in the two non-active harddrive for it to be inactive on the bus. I remember that it was 2-3, and not the 50/80-pins.

Any one that can shead some light on this?

/Johan Ch
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  1. It seems to me you'd run into problems with the BIOS improperly recognizing the drives? They would have to be identical, and even then I'm not sure how Windows would react to the drive volume suddenly switching. I know that even external USB/Firewire drives that are built for hot swapping easily get corrupted files if you just pull them out without telling windows the hardware is being removed. You can't do that for internal ATA drives at all, so you'd get "delayed write failed" errors and corrupted files.

    This might be more easily done with hot-swappable enclosures or properly set up NTFS permissions in Win XP or 2000. You can easily prevent one user from changing another user's files with file permissions, and with a hot-swap enclosure you can put the "active" student's hard drive in the PC and keep the other students' drives in a drawer. You'd have to be the only one with access to that switch anyway, so it would have to be inside the PC. You'd save time using the other methods and not having to open the PC to switch students.

    Just go for Serial ATA, because hot swapping works much, much better with that. (It's built in to the standard I'm pretty sure. Not standard at all for normal flat ATA cables.) Parallel ATA hot-swap can work, but you need a controller supporting it, and you need to VERY carefully select your enclosures and drives, because different P-ATA drives have connectors in different positions. Cheap SATA controller, three small SATA hard drives, and a hot swap enclosure, and you're set, because the SATA connector positions are standardized.
  2. Well, first of I might have been a bit unclear in my initialy post.

    I never said that the drives should be hot-swaped. That's a completely different thing than what I proposing. I want to swap the drives when the computer is turned of. In fact, my intention was even to prevent switching drives when the computer is turned on.

    Next, I don't see how this would be a problem for the BIOS since we use auto detect today. The meaning is that from the BIOS point of view, it would look like another drive have been installed. Looking at it from Windows, it woulden't be any problem at all since it would boot from the currently active drive, the sam drive that this specific installation was installed onto. It would look like that while the computer was turned of, someone replaced the primary master drive.

    Using NTFS permissions? Well, this dosen't prevent a student from deleting the wrong partition on the drive when installing the Windows that he is going to work with, and destroying everyone elses work in this computer.

    Prevent everyone from switching drives? That's easy! Ever heard of keyswitches?

    Any one that chould shade some light on this matter? The question is: Do I have to disconnect all the 50 pins between the harddrive and IDE controler for the drive not to be recognised?

    /Johan Ch
  3. Hey, I have a SCSI drive rack that does that, but I've never seen an IDE enclosure that could be switched "off" like the SCSI enclosures. Rather, the key on IDE enclosures I've used has always only controlled whether or not the drive was removable.

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  4. Quote:
    I never said that the drives should be hot-swaped. That's a completely different thing than what I proposing. I want to swap the drives when the computer is turned of. In fact, my intention was even to prevent switching drives when the computer is turned on.

    Yes, that makes a lot of difference - a switch would work fine under those circumstances, and the BIOS would auto-detect just fine. Your only problem would be rewiring and resoldering the cables without destroying the signal integrity. Remember that to achieve ATA66 and above, they had to apply transmission line theory and introduce signal/ground pairs in the cables. Separating those may cause problems, so watch out for that if you are set on that switch idea.

    But, what I suggest is these:
    <A HREF="http://www.rackmountnet.com/rmc/c_accessories/hddmodules/hddmodules.htm#BR-23" target="_new">http://www.rackmountnet.com/rmc/c_accessories/hddmodules/hddmodules.htm#BR-23</A>
    except the single-drive configuration, if you can find it. It exists, I know that for sure, and it really is an excellent hot-swap bay. You don't need to hot swap of course - but it has a key lock, and will work well without any signal integrity issues, saves you soldering time and debug time for a custom-hacked circuit in your PC, and you can buy extra trays for it. There are SATA versions as well, and some drive trays will even convert PATA -> SATA to plug PATA drives in to a SATA backplane, if that is a benefit for you at all.

    And yes, NTFS permissions would not work if your class works with the pre-boot environment and bootable installation CDs.

    question, since you really seem interested in the keyswitch - do you even have a keyswitch that is single-pole-triple-throw, and has more than two or four pins? I haven't ever seen a keyswitch that could switch even 6 to 8 pins at once, much less 50, and you can't separate the signal-ground pairs and only switch the signal wires or the cables won't work... Search around for IDE or ATA pin definitions. I have seen websites that give the actual signal names of each wire in the cable, but I have to head to work so I can't look right now.

    --- oops last minute addition --
    I found the single drive carrier for you. It's on this page:
    <A HREF="http://www.rackmountnet.com/rmc/c_accessories/tray/tray.htm" target="_new">http://www.rackmountnet.com/rmc/c_accessories/tray/tray.htm</A>
    The single drive tray is the <A HREF="http://www.rackmountnet.com/rmc/c_accessories/tray/br-mbp.jpg" target="_new">BR-MBP</A>, and the <A HREF="http://www.rackmountnet.com/rmc/c_accessories/tray/trayide.jpg" target="_new">TRAY-IDE</A> is the extra tray that fits. I have some of these in one of my computers, and I actually ordered them from that company, so they're pretty good. The company even handled a return/exchange from another drive tray type that was only compatible with WD drives for some reason, and handled it very well, so you can trust to order from them. And that tray doesn't have hard-drive manufacturer compatibility issues. If you look at the screws that attach the PCB to the back of the tray, you can see that they are in wide slots not holes, to make the position of the drive connector adjustable.
  5. Regarding the switch question, I have a supplyer stock 4-way, 1-pol keyswitches. The rest of the pins would be switched with a simple logic circut.

    About the signal path, that crossed my mind also. I don't know how to solve that. One way would be to place the logic curcit almost "in" the IDE connector going to the drive, and keep the cable as short as possibel. I have to test how sensetive this realy is....

    Any way. Thanks for the tip with the drive bay. That would actually work greate. I have used these in the past, but it diddent cross my mind at this point....

    I have some testing and consideration to do here....


    ------ Additional posting ------
    I actually went through all my old stufe, and found a one drive unit, very much like the one you sugested. I took a closer look at the curcit board and founf out that the switch only cuts the power to the drive. I wounder if that's enough. If a connect two drives to the same IDE channel and set both of the drive as MASTER, and just connect power to one of the. Would the BIOS only see the powered drive?

    This have to be tested at once!!!
    <P ID="edit"><FONT SIZE=-1><EM>Edited by JohanCh on 09/02/04 02:39 PM.</EM></FONT></P>
  6. I think that if you crimped additional IDE connectors onto the end of a single IDE cable, the presence of one IDE drive's data connector on the wire might interfere with the other's signal. That's a might - if it works it works, if it doesn't that's probably why.

    About your logic circuit idea - make sure you know enough about how these things work to select components that switch fast enough to carry that signal. You should probably force the BIOS to run drives in ATA66 or ATA100 mode if you insert new components along the signal path, just to be safe. (remember that ATA133 is the fastest speed they have currently managed to get out of parallel ATA cables. Which tells me that the signal quality might be close to some kind of limit.) I don't think most of the 7400 type chips you can buy are capable of operating in the upper MHz range, but I suppose it's possible.

    I still think your best bet is to give each student a drive, either to keep with them or to keep in your drawer, and have each student put his/her drive in the bay when working. It's standard, requires no extra work on your part, and is guaranteed to work. All you have to do is keep the key with you.

    One thing about the hot-swap bays I mentioned. The keys do NOT turn the drive off on those enclosures. The drive can still function when it is not locked in. So, to prevent students swapping another student's drive for their own, either you would have to be the only one with access to the place the drives are kept, or each student would have to keep their own drive (and worry about dropping it.)

    Enclosures do exist that turn the drive off when the key is turned though, preventing anyone from inserting a drive without the key.
  7. All these guys have some great ideas :eek: but I have seen, and even used, a HDD switch that can connect 3 hard drives, and is unable to switch HDD when the computer is on, and can be used for booting multiple systems.

    <A HREF="http://www.hardocp.com/article.html?art=MTk3" target="_new">Here</A> is a good article on them. They are called Romtec Trios. The only problem is the web page doesn't seem to be working for Romtec.

    If they aren't available commercially anymore, I'm sure you can find something similar/find them on e-bay.

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  8. That is a good idea, I have not heard of this though.
    If you are using XP pro, you could set up profiles, set each student as user, and then they could not edit system settings, nor access other users data. This would be simpler and cheaper.
    Also, could just move the cable on the drives each time for different students.
    Or boot from external USB or Firewire drive through BIOS, this would accomplish same thing.

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