1) Is is also possible to add a 3rd harddrive via USB or Firewire to the
RAID1 and then using your idea to detach and reattach the harddrive?
yes, that is a very good method. I suggest you try to do esata but usb or
firewire will work. esata is just much faster.
2) When I attach the harddrive to my RAID 1, is md smart enough to just
transfer the changes to the attached drive or will it make a full sync?
(sorry for this newbie question)
it is smart enough to only read identical blocks on the disk and only write
changed blocks. you still have to wait, at a minimum, the time it takes to
do an entire sequential read of the disk plus the time to write the changes
to the disk.
other stuff
iscsi:
you do not have to have any kind of high end fancy iscsi SAN, you can make
an iSCSI target with a regular linux machine. iSCSI is not terribly hard to
setup, but you would need some sore of dedicated equipment, either a small
server or a stand alone device.
AoE: another very very handy solution is ATA-over-Ethernet. It is
something like iscsi but is not a protocol on top of IP, it is a protocal on
the same level as IP. That means that you cannot route it between networks
which could be considered a negative but the BIG positive is that you need
ZERO IP configuration.
When you make an AoE server, you export disks with a "shelf" + "slot"
topology that is carried over to each machine that sees the AoE.
For example. on your linux server, you do AoE with a program called vblade
and you make a disk vblade 0 0 which is shelf 0 slot 0. you can then do
another disk that is shelf 0 slot 1. on another server you can do a shelf 1
slot 0 and so on.
on every single machine that can see the AoE disks(because they have the aoe
module running) they all see the same drives with the same ID.
/dev/etherd/e0.0 for shelf0slot0 /dev/etherd/e0.1 for shelf0slot1.
on your backuppc server, you can add /dev/etherd/e0.1 to the mirror, you
could even add two AoE disks or more to the mirror if you desired. You can
even export AoE disks(with vblade) that are just disk images.
The beauty of this system is that the backuppc server can be on a server
rack and all the hot swapping of drives can be done on a linux machine
somewhere else. this happens buy exporting a USB drive on the linux machine
via AoE and having backuppc watch for the AoE disk and running the
appropriate mdadm script. If you really wanted to get creative, you could
run linux in a vmware vm and tie a specific USB port to that vm, now you can
export the USB disk over AoE on linux, while running WinXP on your desktop.
ubuntu server with AoE can run in a 128MB of ram vm quite well.
AoE works without IP overhead so is very fast. near-wire speeds on 100Mb
ethernet or even gigabit.
Maybe I'm crazy, I don't know!
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