David Abrahams <[EMAIL PROTECTED]> writes: > Daniel Pittman <[EMAIL PROTECTED]> writes: >> David Abrahams <[EMAIL PROTECTED]> writes: >> >>> I recently bought a pair of SATA drives on which to do weekly backups >>> of my server. I also got a cool drive tray that allows me to pop the >>> disks in and out of the machine easily: >>> http://www.cooldrives.com/sata-serial-ata-mobile-rack-enclosure-lcd.html >>> You can remove the drive from the machine by turning a key -- which >>> powers it down -- and pulling on the handle. >>> >>> My problems: >>> >>> 1. If I boot the server with no drive in the bay or with the drive >>> power off, it is never detected, even after powering it on. Is >>> there a way to get that to work?
[...] >> Sadly, none of that seems completely clear about what kernel release is >> required for the various hot-plug and warm-plug options to work. You >> may be forced to resort to asking the linux-kernel mailing list if >> someone else here can't chime in. > > Also, none of that is clear about what, exactly, constitutes "support > for hot-swap" (which is connected with my next question). Well, one key point is your issue above: while the hardware (probably) issues an interrupt when the new hardware is connected, Linux ignores that rather than detecting the device. That would be one part of hot-swap - the hot-add case. >>> 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. 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. Also, if you don't stop the drive spinning before you pull it then you have cut power to a disk in rotation. 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. >>> 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. > > 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. 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. Regards, Daniel -- Digital Infrastructure Solutions -- making IT simple, stable and secure Phone: 0401 155 707 email: [EMAIL PROTECTED] http://digital-infrastructure.com.au/ -- ubuntu-server mailing list ubuntu-server@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-server