On Wed, Nov 20, 2019 at 9:36 AM Christian Pernegger <pernegger@xxxxxxxxx> wrote: > > Hello, > > I've decided to go with a snapshot-based backup solution for our new > Linux desktops -- thank you for the timely thread --, namely btrbk. > A couple of subvolumes for different stuff, with hourly snapshots that > regularly go to another machine. Brilliant in theory, less so in > practice, because every time btrbk runs, the box'll freeze for a few > seconds, as in, Firefox and LibreOffice, for instance, become entirely > unresponsive, games hang and so on. (AFAICT, all it does is snapshot > each subvolume and delete ones that are out of the retention period.) > > I'm aware that having many snapshots can impact performance of some > operations, but I didn't think that "many" <= 200, "impact" = stop > dead and "some operations" = light desktop use. These are decently > specced, after all (Zen 2 8/12 core, 32 GB RAM, Samsung 970 Evo Plus). > What I'm asking is, is this to be expected, does it just need tuning, > is the hardware buggy, the kernel version (Ubuntu 18.04.3 HWE, their > 5.0 series) a stinker, something else awry ...? What are the mount options? And what's the workload immediate prior to the snapshot? Or does it always happen no matter the workload? I use Btrfs on a variety of hardware and storage devices, USB flash, NVMe, hard drives, and a Samsung 940 EVO, and I can't say I experience anything like a freeze or hang. If I'm doing something like updates (dnf updates, RPM) and do a snapshot while the update is happening (bit kooky because that snapshot represents an inbetween state of the update, essentially useless except as an intentionally poking things with a stick just to see what happens) I do see a user space "hang" as a flush is required as part of the snapshot, and I see this flush using top. But so far I only see it affect the snapshot command itself (it's a delay rather than a hang). I don't see it affect GUI responsiveness. -- Chris Murphy
