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RE: [Xen-users] hotplug Backup-hdd

To: "Tegger" <xen@xxxxxxxxx>, "Xen Users" <xen-users@xxxxxxxxxxxxxxxxxxx>
Subject: RE: [Xen-users] hotplug Backup-hdd
From: "James Harper" <james.harper@xxxxxxxxxxxxxxxx>
Date: Mon, 27 Sep 2010 17:27:59 +1000
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Thread-topic: [Xen-users] hotplug Backup-hdd
> i have a system with
> /dev/sda - System Hard Drive
> /dev/md0 - SoftwareRaid 5 for Data
> with
> /dev/sdb
> /dev/sdc
> /dev/sdd
> Now i have one more in a removeable frame for Backup
> /dev/sde
> /dev/md0 is forwarded to an Samba-Domain for Data service in the
> What's the best way to sync the data from /dev/md0 to /dev/sde ?
> is a domain hotplug able ? So when i plug in /dev/sde, it's automatic
> forwards to Samba domain, is this possible ?

'xm block-attach' and 'xm block-detach' are the commands to plug and
unplug devices from a DomU. You should be able to do this automatically
via udev - make a rule that identifies your device by serial number or
path (/dev/disk/by-id/... or /dev/disk/by-path/...) and make a RUN +=
command that does the 'xm block-attach', and the opposite on unplug. Not
sure if you're asking for trouble with the unplug though - domu might
get upset when the underlying device goes missing before it is unplugged
from the domain.

As I hinted above, it really is best to use /dev/disk/by-id/ or
/dev/disk/by-path/ to be absolutely sure that you have the right device.
If you attach an eSATA device one day and it bumps all your devices up
by one (eg /dev/sdd becomes /dev/sde) then you'll suddenly have one of
your RAID devices attached to your DomU instead, and nothing good will
come of that.

/dev/disk/by-id/... is useful when you want a specific physical disk as
you can refer to it via make, model, and serial number.

/dev/disk/by-path/... is useful when you want to refer to a disk plugged
into a specific USB port (unless your USB adapters are enumerated in
random order... then you're screwed!). I do this will USB backup disks.


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