Hi Lawrence,

With regard to a wlug presentation...

I was thinking along the lines of a laptop plugged into the overhead projector with its main partition for Linux and, say, 2 x 1GB partitions of dummy data in a mirror-set. Then also have one or two USB sticks which have 1GB partitions on them that can be plugged into the laptop and join the mirror-set.  

> Can Ian provide hardware failures?

The failure scenario I envisage would be to pull out a USB stick and observe the remainder of the mirror-set still works OK. Plug in a USB stick and observe the merging of the member back into the mirror-set.

Do you think that would be OK? Would 1GB partitions take too long to sync in a demo situation? Would, say, 100MB partitions be more suitable?

I have one of Ian Young's Thinkpad laptops that works good with the overhead projector. I don't think Ian would mind if you used it to demo Linux RAID. It's got Ubuntu/Mate 15.04 on it at the moment. Let me know what is your preferred flavour of distro/desktop and I'll install it. I'd add GParted for use in generating same sized partitions. Any other apps you'd want added?

> Note I have only used RAID-1

I figure that RAID-1 is all that most people would be interested in as a single member, removed from the mirror-set, can be demoed as a backup device.

> But you canít be sure that syncing has finished when you want to unplug.

Is there a way to monitor the degree of completion of syncing of an added member to the mirror-set?

It's now more than 15 years ago that I used DEC's OpenVMS RAID-1 called Volume Shadowing, but I recollect that they had a feature called "mini-merge" as opposed to "full-merge". My understanding was that mini-merge would find the files that had changed and only update them as part of the syncing when a member gets added back to the mirror-set, whereas "full-merge" was a block by block merging process. Does Linux RAID have this sort of "mini-merge" functionality?

> I have a custom script that uses rsync to back up between volumes.

It would be good if you could also demo this. It may highlight that rsync is a better way of doing backups than pulling a member off a mirror-set.

cheers, Ian.