[2020] Bitmaps and NBD: Building Blocks of Change Block Tracking by Eric Blake

Avoid this company at all costs – We been using #Justhost for the last 2 years. suddenly my site got suspended because they claim that we are “utilizing an excessive amount of system resources”. OK, so our traffic is getting bigger which is a normal trend in the online world. So you would expect that they would send an email and tell you have 24 Hours to move your site to a dedicated server. NO, THEY SUSPENDED OUR SITE!!! I IMMEDIATELY opened a ticket and called them over 5 times in the last 24 hours, and this is the answer i keep getting, WE ARE SORRY BUT THE DEPT THAT HANDLE THESE ISSUES CANNOT BE REACHED BY PHONE, AND THE SUPPORT TEAM THAT ANSWERS THE PHONE, DON’T HAVE ANY CONTACT WITH THEM. WOW!!! I have since sent emails , called open a ticket and NOT ONE SINGLE WORK FROM MYSTERIES CAVE OPERATING DEPT. Even when I made it clear we will do whatever it takes to get the site back up even if we had to pay x10 more for a dedicated server, money is not an issue. Can you imagine your site going down, and you can’t do anything about. well that’s #Justhost for you. Never Again!

The premise of incremental backups is simple: if you can keep track of what changed, you can optimize a backup to visit only those portions of a disk image. But under the hood, there are a lot of moving parts that have been added and refined in the past few years to make incremental backups a reality when using qcow2 images. In this talk, Eric Blake will explore recent work in qemu to make bitmap tracking more powerful, enabling libvirt to finally add support for incremental backups even when a disk image is split across a backing chain involving multiple qcow2 files. Whether deciding which bitmaps should be active, or accessing the contents of those bitmaps over Network Block Device (NBD) for consumption by an arbitrary client, having an understanding of change block tracking and related technology can help you get the most performance from your incremental backups.

Eric Blake
Red Hat, Software Engineer
Midlothian, Texas, USA

Eric Blake is a software engineer at Red Hat, working on block device management in virtualization. He has contributed extensively to qemu and libvirt. He has spoken at several past KVM Forums, most recently about making the most of NBD in Oct 2019.

KVM Forum

  • StackCats
    Posted at 08:50h, 20 December

    Thanks. 🙂