[ILUG] Hot swap drive?

[Niall O Broin]

On Thursday 22 July 2004, c.daly at met.ie (Conor Daly) wrote:

>Can I, while up and running, plug in the disk, do 'mount /dev/hdXX
>/mnt/point', rsync (or whatever), 'umount /mnt/point', unplug the disk?
>
>Or do I have to power off for the plug / unplug stages?
>
>In other words, does 'hot swap' mean "you can plug / unplug a mounted drive
>and all will be fine" or does it mean "you can plug / unplug a drive so long
>as it's not mounted at the time"?

Possibly, maybe, who knows. 

But the real answer has to be no, I'm afraid. You can't really hot plug IDE
because the system doesn't know the drive is there. When it boots, it doesn't
find a drive, and then you add one in - how is it to know it's there? If you
have two identical drives, and you want to swap them, it MAY work but you may
still have problems when you plug and unplug the device. Being able to do that
correctly requires tri state buffers which you probably WON'T get on a cheap
caddy from Marx.

Oh - you certainly CAN'T unplug a mounted drive, no matter what the hardware
arrangements, without risking massive FS corruption. Always umount first. Kate
tells a nice story about an SA in a certain large company, anxious to
demonstrate his shiny Sun RAID system with hot plug drives, unplugged some
drives without informing the OS of his intentions. This did nothing but bad to
the database which was using the disks at the time.

A better option might be an external USB-2 (USB is rather slow for a big
drive) or Firewire drive. If your box doesn't have USB-2 or Firewire, add-in
cards are relatively cheap.


Niall