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Instability with NetBSD Dom0
For a couple of years, I've been using NetBSD as a Dom0 with various
versions of Xen. Most of the time, I've given DomU systems disk through
plain sparse files on the Dom0 (i.e., not as hard partitions).
I have seen some stability issues (freezes) over the years when the Dom0
needed lots of CPU, e.g., as a result of DomU I/O. But since my
installations where physically nearby, I could simply power cycle the
systems when this happened.
Now, I decided to deploy a large system which is co-located...
The system has two disks:
* wd0 has Xen and NetBSD plus 200 GB for various DomUs. These DomUs are
for testing but also for critical services in DMZ, and name servers,
etc. This is a 240 GB Samsung SM843Tn (an "enterprise" SSD).
* wd1, has FreeBSD raw on the disk (and running as a HVM DomU). This is
a 480 GB Samsung SV843T (also an "enterprise" SSD).
NetBSD is 7.0 BETA and Xen is 4.5, both from about a week ago. The
machine is a 6 core Ivy bridge Xeon in a Supermicro system.
All was fine until tonight. Now I cannot reach the Dom0 nor any DomUs
which live on wd0. I can still reach the FreeBSD guest, in fact it
seems completely unaffected.
What appeared to have triggered the problem was a write operation to a
20 GB file, a file which is created in the Dom0. The following
operations were performed (the variable 'reldir' points to a release
qemu-img-xen create -f raw disk.img 20G
vnconfig -c vnd16a disk.img
newfs -O2 /dev/vnd16a
mount -o discard,log,noatime /dev/vnd16a /mnt
df | grep "$mntpt"
for i in base.tgz comp.tgz etc.tgz; do
tar -x -z -f $reldir/sets/$i -C /mnt
I know the script reached the df command as the output is visible at the
hung terminal. The 'echo foo' line is never reached.
(I know that /mnt was priorly unused, and that vnd16 was free.)
I have performed perhaps 15 installs with the above operations, but they
all were small (1 GB image). No problems there.
Please advise me. I need this system to be very stable. The system it
is about to replace runs FreeBSD with jails, a solution which I want to
avoid as FreeBSD is moving in a direction I cannot handle. I really
really would want to run Xen + NetBSD on the new system.
Some specific questions:
(1) Would you agree that using plain files for DomUs tend to lead to
(2) I have never used NetBSD's LVM, but would that lead to greater
stability? Carving up the disk (wd0) using a plain old NetBSD
disklabel wouldn't work, as I have some 30 DomUs.
(3) Else, how can I place many DomUs on the disk such that the Dom0 is
not involved? Carving up the disk with with a DOS MBR into 7
partitions, and then place a NetBSD label on each? Irksome, but if
that's the only way, I'll cope.
(4) Hand on heart, do you think I can make this system stable? How?
A sensible reaction might be "you run a BETA version of NetBSD and a
BETA integration of Xen 4.5, what did you expect?!". But as a
mentioned, the problem is not unique to these software versions; I have
seen similar issues with NetBSD 6.1.x + Xen 4.2.y (although not with a
Please encrypt, key id 0xC8601622
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