I’ve been meaning to write about this for a while and since it’s come up recently (Write Intent Bitmaps, Software RAID) I figured now would be a good time. Basically what the write-intent bitmap does is keep track of which blocks are being used so that in the event that a resync is needed (power failure, kernel crash, disk temporarily offline) only the blocks that are out of sync are copied. This drastically improves resync times. Of course there is a downside.

I’ve been experiencing some issues with regard to backing up my Xen user domains. As I investigated the issues I once again found the lack of documentation to be frustrating, especially about such a fundamentally important issue as backups. There is simply no documentation on how to setup enterprise level backups for Xen. So here on some thoughts on what I see as the state of things, and where they could go form here to get better.