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#11
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"Timothy Daniels" wrote:
It would be a lot easier if one could just shut down and then disconnect the other drives by use of a physical switch to break the connection with their power cables. That would avoid all the hassle of opening the case and unplugging the other drives. So, does anyone have any information that would indicate if switching the power cables would work? I'd be very surprised if you get away with that. Having un-powered electronics connected to your bus is generally a sure-fire way to drag the bus down to nothing. This is why hot-swap devices, whether they are USB or whatever, have connectors that ensure that the power is applied before the signals are connected. |
#12
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"chrisv" wrote: "Timothy Daniels" wrote: It would be a lot easier if one could just shut down and then disconnect the other drives by use of a physical switch to break the connection with their power cables. That would avoid all the hassle of opening the case and unplugging the other drives. So, does anyone have any information that would indicate if switching the power cables would work? I'd be very surprised if you get away with that. Having un-powered electronics connected to your bus is generally a sure-fire way to drag the bus down to nothing. This is why hot-swap devices, whether they are USB or whatever, have connectors that ensure that the power is applied before the signals are connected. I was *not* asking about a hot-swap wherein the logical state of the drive would be undefined when powered was applied by virtue of the signal cables being pre-connected. I *was* asking about doing the switching ON/OFF of power cables while the PC was shut down. This would be logically equivalent to physically connecting and disconnecting the power cables to various HDs by opening the case, etc. I know this works in some configurations - single HDs on separate channels - because I've done it. That is, just disconnecting the power cable of one HD allows the other HD (on the other IDE channel) to boot up in isolation. My question really hinges on the effect of unpowered devices connected in various combinations and configurations to a 2-device IDE cable. What would happen if the Master HD at the end of a cable were unpowered while the Slave were powered? If the Slave were unpowered and the Master powered? If Master/Slave positions were reversed? Etc., etc. Assuming that the signals "see" a high input impedance at the HD's circuit card, I'm guessing it wouldn't make a difference to the channel controller whether the circuitry of the card were powered on unpowered, i.e. at boot-up, the BIOS would not see the unpowered device, and the IDE controller wouldn't try to talk to it, and the dead circuit card's high input impedance would not drain signals passing by it. *TimDaniels* |
#13
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"chrisv" wrote in message news "Timothy Daniels" wrote: It would be a lot easier if one could just shut down and then disconnect the other drives by use of a physical switch to break the connection with their power cables. That would avoid all the hassle of opening the case and unplugging the other drives. So, does anyone have any information that would indicate if switching the power cables would work? I'd be very surprised if you get away with that. Having un-powered electronics connected to your bus is generally a sure-fire way to drag the bus down to nothing. It does work most of the time with removable drive bays. This is why hot-swap devices, whether they are USB or whatever, have connectors that ensure that the power is applied before the signals are connected. Nope, thats for a completely different reason. And what they do is ensure that GROUND is connected first on insertion and disconnected last on removal. |
#14
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"Timothy Daniels" wrote in message ... "chrisv" wrote: "Timothy Daniels" wrote: It would be a lot easier if one could just shut down and then disconnect the other drives by use of a physical switch to break the connection with their power cables. That would avoid all the hassle of opening the case and unplugging the other drives. So, does anyone have any information that would indicate if switching the power cables would work? I'd be very surprised if you get away with that. Having un-powered electronics connected to your bus is generally a sure-fire way to drag the bus down to nothing. This is why hot-swap devices, whether they are USB or whatever, have connectors that ensure that the power is applied before the signals are connected. I was *not* asking about a hot-swap wherein the logical state of the drive would be undefined when powered was applied by virtue of the signal cables being pre-connected. I *was* asking about doing the switching ON/OFF of power cables while the PC was shut down. This would be logically equivalent to physically connecting and disconnecting the power cables to various HDs by opening the case, etc. I know this works in some configurations - single HDs on separate channels - because I've done it. That is, just disconnecting the power cable of one HD allows the other HD (on the other IDE channel) to boot up in isolation. My question really hinges on the effect of unpowered devices connected in various combinations and configurations to a 2-device IDE cable. What would happen if the Master HD at the end of a cable were unpowered while the Slave were powered? The short story is that there doesnt need to be a Master at all. You see that quite a bit with CD drives as the only drive on a ribbon cable and most hard drives work fine in that config now too. The problem is potentially with an unpowered drive physically connected to the ribbon cable, not the master/slave question. If the Slave were unpowered and the Master powered? If Master/Slave positions were reversed? Etc., etc. Its all irrelevant. What matters is if there is a drive which isnt powered plugged into the ribbon cable. Assuming that the signals "see" a high input impedance at the HD's circuit card, I'm guessing it wouldn't make a difference to the channel controller whether the circuitry of the card were powered on unpowered, i.e. at boot-up, the BIOS would not see the unpowered device, and the IDE controller wouldn't try to talk to it, and the dead circuit card's high input impedance would not drain signals passing by it. That last is the problem, the unpowered ics on the ribbon cable. |
#15
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"Rod Speed" wrote:
"Timothy Daniels" wrote: My question really hinges on the effect of unpowered devices connected in various combinations and configurations to a 2-device IDE cable. What would happen if the Master HD at the end of a cable were unpowered while the Slave were powered? The short story is that there doesnt need to be a Master at all. You see that quite a bit with CD drives as the only drive on a ribbon cable and most hard drives work fine in that config now too. The problem is potentially with an unpowered drive physically connected to the ribbon cable, not the master/slave question. Right. I meant a dead device at the *usual position* of a Master (at the end of the 2-device cable) and the *usual position* of a Slave (at the mid connector of the cable). My assumption has been that the roles of Master and Slave on the same channel were only for device differentiation for the IDE channel controller. Please correct me if that is wrong. If the Slave were unpowered and the Master powered? If Master/Slave positions were reversed? Etc., etc. Its all irrelevant. What matters is if there is a drive which isnt powered plugged into the ribbon cable. Right. Again, I meant the effect of dead (unpowered) devices at the *usual positions* of Master and Slave. IOW, does a dead device at either position on the ribbon cable upset the signals for the other device? BTW, does is matter a whit if there are 2 devices (e.g. HDs) on a cable and the device jumpered "Master" is at the mid connector and the device jumpered "Slave" were at the end connector? I have been assuming that there is no difference other than which device will default to being the boot device. Is that correct? Assuming that the signals "see" a high input impedance at the HD's circuit card, I'm guessing it wouldn't make a difference to the channel controller whether the circuitry of the card were powered on unpowered, i.e. at boot-up, the BIOS would not see the unpowered device, and the IDE controller wouldn't try to talk to it, and the dead circuit card's high input impedance would not drain signals passing by it. That last is the problem, the unpowered ics on the ribbon cable. Yup. That's the question, too. :-) *TimDaniels* |
#16
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"Timothy Daniels" wrote:
"chrisv" wrote: "Timothy Daniels" wrote: It would be a lot easier if one could just shut down and then disconnect the other drives by use of a physical switch to break the connection with their power cables. That would avoid all the hassle of opening the case and unplugging the other drives. So, does anyone have any information that would indicate if switching the power cables would work? I'd be very surprised if you get away with that. Having un-powered electronics connected to your bus is generally a sure-fire way to drag the bus down to nothing. This is why hot-swap devices, whether they are USB or whatever, have connectors that ensure that the power is applied before the signals are connected. I was *not* asking about a hot-swap wherein the logical state of the drive would be undefined when powered was applied by virtue of the signal cables being pre-connected. I *was* asking about doing the switching ON/OFF of power cables while the PC was shut down. I didn't think you were trying to hot-swap. I just threw that in as an example of the importance of never having signals connected to un-powered devices. This would be logically equivalent to physically connecting and disconnecting the power cables to various HDs by opening the case, etc. I know this works in some configurations - single HDs on separate channels - because I've done it. That is, just disconnecting the power cable of one HD allows the other HD (on the other IDE channel) to boot up in isolation. It's not surprising that you can get away with it when there's nothing else on that bus that needs to work... My question really hinges on the effect of unpowered devices connected in various combinations and configurations to a 2-device IDE cable. What would happen if the Master HD at the end of a cable were unpowered while the Slave were powered? THAT is what I don't think will work. Rod says it will, and maybe it will, for some controller/HD combinations. But it's quite hokey to do that, even if you get away with it. If the Slave were unpowered and the Master powered? If Master/Slave positions were reversed? Etc., etc. Assuming that the signals "see" a high input impedance at the HD's circuit card, That's a big assumption. I'm guessing it wouldn't make a difference to the channel controller whether the circuitry of the card were powered on unpowered, i.e. at boot-up, the BIOS would not see the unpowered device, and the IDE controller wouldn't try to talk to it, and the dead circuit card's high input impedance would not drain signals passing by it. |
#17
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Timothy Daniels wrote in message ... Rod Speed wrote Timothy Daniels wrote My question really hinges on the effect of unpowered devices connected in various combinations and configurations to a 2-device IDE cable. What would happen if the Master HD at the end of a cable were unpowered while the Slave were powered? The short story is that there doesnt need to be a Master at all. You see that quite a bit with CD drives as the only drive on a ribbon cable and most hard drives work fine in that config now too. The problem is potentially with an unpowered drive physically connected to the ribbon cable, not the master/slave question. Right. I meant a dead device at the *usual position* of a Master (at the end of the 2-device cable) and the *usual position* of a Slave (at the mid connector of the cable). Thats only true of a cable select cable. It doesnt matter which drive is on which connector with a master/slave config. My assumption has been that the roles of Master and Slave on the same channel were only for device differentiation for the IDE channel controller. Cant see what the relevance of that is to what is being discussed. Please correct me if that is wrong. If the Slave were unpowered and the Master powered? If Master/Slave positions were reversed? Etc., etc. Its all irrelevant. What matters is if there is a drive which isnt powered plugged into the ribbon cable. Right. Again, I meant the effect of dead (unpowered) devices at the *usual positions* of Master and Slave. IOW, does a dead device at either position on the ribbon cable upset the signals for the other device? Nope, makes no difference. The only difference the position makes is when there is just one drive on the ribbon cable and the end connector has nothing connected to it. In that situation the unused bit of the ribbon cable is a stub and you can get a reflection off the unconnected end with digital signals. But an unpowered drive on that end connector should stop most of that. BTW, does is matter a whit if there are 2 devices (e.g. HDs) on a cable and the device jumpered "Master" is at the mid connector and the device jumpered "Slave" were at the end connector? Nope, thats fine. The only undesirable config is with just one drive on the ribbon cable, and that drive on the middle connector. In that case you have a length of ribbon cable going nowhere and that can produce reflections on the cable with digital signals. I have been assuming that there is no difference other than which device will default to being the boot device. Is that correct? It wont even affect which drive is the boot device. That is determined by which drive is specified as the boot drive in the bios and has nothing to do with which is master or slave or which physical connector its connected to with a master/slave config. It does matter with a cable select config where the master and slave is determined by which connector the drive is connected to and not the jumpering on the drive. Assuming that the signals "see" a high input impedance at the HD's circuit card, I'm guessing it wouldn't make a difference to the channel controller whether the circuitry of the card were powered on unpowered, i.e. at boot-up, the BIOS would not see the unpowered device, and the IDE controller wouldn't try to talk to it, and the dead circuit card's high input impedance would not drain signals passing by it. That last is the problem, the unpowered ics on the ribbon cable. Yup. That's the question, too. :-) |
#18
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"Rod Speed" wrote:
"chrisv" wrote in message news "Timothy Daniels" wrote: It would be a lot easier if one could just shut down and then disconnect the other drives by use of a physical switch to break the connection with their power cables. That would avoid all the hassle of opening the case and unplugging the other drives. So, does anyone have any information that would indicate if switching the power cables would work? I'd be very surprised if you get away with that. Having un-powered electronics connected to your bus is generally a sure-fire way to drag the bus down to nothing. It does work most of the time with removable drive bays. I'm not familiar with these... Are you saying they leave multiple drives connected to a bus, with some of those drives not powered? This is why hot-swap devices, whether they are USB or whatever, have connectors that ensure that the power is applied before the signals are connected. Nope, thats for a completely different reason. Well, it allows the device's reset circuitry to bring things to a known state, as well... I don't think your "nope" is warranted, however. And what they do is ensure that GROUND is connected first on insertion and disconnected last on removal. Maybe with some hot-swapable devices, but not all. USB clearly connects power and ground at the same time, as does Compact PCI (cPCI). http://www.intersil.com/data/tb/tb386.pdf http://www.quicklogic.com/images/cpci.pdf |
#19
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chrisv wrote:
"Timothy Daniels" wrote: My question really hinges on the effect of unpowered devices connected in various combinations and configurations to a 2-device IDE cable. What would happen if the Master HD at the end of a cable were unpowered while the Slave were powered? THAT is what I don't think will work. Rod says it will, and maybe it will, for some controller/HD combinations. But it's quite hokey to do that, even if you get away with it. If the Slave were unpowered and the Master powered? If Master/Slave positions were reversed? Etc., etc. I should have noted that switched master and slave around is irrelevant to this situation. |
#20
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"chrisv" wrote:
"Timothy Daniels" wrote: My question really hinges on the effect of unpowered devices connected in various combinations and configurations to a 2-device IDE cable. What would happen if the Master HD at the end of a cable were unpowered while the Slave were powered? THAT is what I don't think will work. Rod says it will, and maybe it will, for some controller/HD combinations. But it's quite hokey to do that, even if you get away with it. Hey! The whole scheme is hokey, including the removable drive tray/rack. I just want to know if it *works*. If it works, it would save a whole bunch of labor, and it would encourage me to do backups more often. *TimDaniels* |
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