Re: Xen storage for NetBSD guests: performance vs. consistent backups (sanity check)

[Matthias Petermann <matthias%d2ux.net@localhost>]

Hi all,

thanks a lot for the many thoughtful replies and perspectives in this 
thread - I found them genuinely helpful.

I wanted to add a short follow-up with a concrete data point, as I had 
the chance today to set up a clean test environment to re-check an issue 
I had observed some months ago.

Test setup:

- NetBSD 10.1_STABLE (built from 2026-01-08), Xen 4.18
- NetBSD Dom0 and identical NetBSD DomU
- DomU filesystem hosted on an LVM volume provided by the NetBSD Dom0
- FFSv2ea + WAPBL as DomU root filesystem
- Backups using dump -X (FSS)

Previously, in essentially this configuration, I had run into 
reproducible freezes during dump -X. With the current setup, however, I 
can no longer reproduce this behaviour.

For reference:

- DomU: 192.168.2.252
- Backup target: USB disk mounted at /mnt
- DomU filesystem ~6 GB used

Tests were run repeatedly and also under mixed load (a bonnie++ load 
test running in parallel inside the DomU)

I did not observe any stalls, hangs, or other instabilities.

The test loop used was:

```
for i in `seq 100 199`; do
  ssh root@192.168.2.252 "/sbin/dump -X -h 0 -b 64 -0auf - /" \
    > /mnt/backup$i.dump
done
```

Under these conditions, the LVM-based approach appears to work reliably 
again and is, at least for me, back to being a viable option.

Many thanks again to everyone for sharing their experiences and insights 
- they were the motivation to revisit and re-test this properly.

Best regards,
Matthias