Daniel, Thank you *very* much for your patient and complete answers. I have a lot to learn and I really appreciate it when someone is willing to take the time to educate me...
Daniel Pittman <[EMAIL PROTECTED]> writes: > David Abrahams <[EMAIL PROTECTED]> writes: >> Daniel Pittman <[EMAIL PROTECTED]> writes: >>> David Abrahams <[EMAIL PROTECTED]> writes: >>> >>>> 2. I'm not 100% sure that unmounting the drive, powering it off, >>>> removing it, and putting a new disk in its place is legit. Can >>>> anyone confirm? My motherboard *does* claim to support SATA >>>> hotswap, but I'm not sure if Linux supports it. >>> >>> Linux probably doesn't, save in the most recent kernels, and possibly >>> only with appropriate patches. >> >> In my case I'm wondering what could possibly go wrong? If the drive >> is completely unmounted before it is powered down and removed, it >> seems as though the OS has no reason to be concerned with how/when I >> plug it in. Any ideas? > > Well, the worst case is that the hardware can short and fry the entire > controller chip, resulting in a dead hard disk, motherboard and > potentially other components. > > That is a pretty bad worst case, but not unknown, for pulling hardware > at random. And seems rather unlikely considering that the motherboard supports SATA hotswap. If I put Windoze on that machine I'd be able to do it. It would be a pretty perverse hardware implementation that would allow you to plug and unplug drives only if the OS were cooperative. > A much more likely fault is that your controller will get to > exercise those wonderful, poorly tested, error handling paths as it > suddenly discovers a missing device. > > That can lead to anything from the controller hanging to a panic when > the error handler turns out to have a bug. Not nice. You're suggesting that the hardware/firmware hotswap handling *itself* (I take it that's what you mean by "the controller") is buggy? > Also, if you don't stop the drive spinning before you pull it then you > have cut power to a disk in rotation. Huh. I guess unmounting the drive isn't enough to stop the spindle. > That necessitates an emergency stop of the heads, which isn't great > for their life. > > Now, it /might/ just work, and if you have hot-swap hardware then the > power issues resulting in physical damage are unlikely. It isn't nice, > and will result in the hardware and the OS believing that a serious > error has just happened. I've already done it once or twice and didn't notice *any* interesting side-effects. But maybe I wasn't looking in the right place. >>>> Lastly, if there's any standard way to automate backup jobs (mounting >>>> disks, rsync or whatever, unmounting, etc.) I'd appreciate a >>>> reference. I can always use cron scripts but I imagine someone has >>>> probably come up with something better. >>> >>> udev can fire off arbitrary code on insertion of a device. You can use >>> that to trigger a script that will, basically, do all the work for you. Are there "standard" scripts for this purpose, or will I be whipping one up at home? >> Is that really what "support for SATA hot-swap" amounts to? > > No. That is the very last bit. Hot-swap is the bit where the OS, > driver, controller and everything else is *aware* that changes are going > to happen, so they can handle them gracefully. > > udev (and hald, and a bunch of other code written on top of those) are > the icing of the cake: when hot-plug works it can react to it sensibly > and do things like configure your new network card, mount your hard > disk, or whatever. > > Hot-swap, as such, is all the bits below that which conspire to make it > work. On a bus like USB this is well tested, while SATA ... isn't. Huh, too bad. Well I did also buy an external hotswapping USB enclosure that I can use, but I was really hoping to get the full speed of SATA for my backups. I guess I just have to weigh that loss against the time it would take to research SATA kernel support and configure/build a new kernel. > Sorry if that wasn't clear to you -- the driver, OS and controller > hardware need to be hot-swap capable for this to have a chance of > working even remotely reliably. Sounds like I've one out of three at the moment. Probably falling back to USB is my best bet in the near term. I need to get the system going and a backup system in place -- that's far more important than having the backups be super fast. Thanks again, -- Dave Abrahams Boost Consulting www.boost-consulting.com -- ubuntu-server mailing list ubuntu-server@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-server
