On Mon, Dec 12, 2016 at 08:33:48AM -0600, Jay West wrote:
> My setup...
> Hosts: Two Dell R310's, each one as follows: 32gb ram, L3480 cpu, 4 gigabit
> nics, two 300gb disks (mirrored), where the local disk is used only to hold
> xenserver 7.0 with all patches up through and including today. These
> machines are 100% up to date on firmware, patches, bios, etc.
> Network: Two Dell powerconnect 6224's, stacked via dual round-robin CX4
> cables. There's an untagged management vlan, an untagged data vlan, and an
> untagged ISCSI vlan - identical ports are members on each switch. On each
> host, the two builtin nics (data) are connected one leg in each switch (same
> vlan). The two addin ports (Intel Pro/1000) (iSCSI) on each host are also
> connected one leg in each switch. The switches are 100% up to date on
> firmware/OS. Client access to this is via a stack of Juniper EX2200's
> trunked back to the 6224's.
> Storage: OEM version of a Tyan 2U 12 bay SAS box, similar to Tyan
> S8226WGM3NR but with 7 gigabit NICS builtin. 32gb ram, FreeNAS 9.10.1-U4,
> and dual AMD C32's (12 cores total). One nic is used for ILO, another for
> management, another is unused , and the remaining four gigabit ports are
> connected two legs in each switch (same vlan, iscsi only, 9000mtu).
> Multipath is configured and active.
> The storage box is using mirrored vdev's with ZFS on top, 100% of which
> present an iSCSI target so the box is doing nothing but iscsi (and an NFS
> iso share for installing vm's). So in Xencenter... there is one storage
> repository containing all the NAS space. Xencenter then creates the vdisks
> inside that for each VM to use.
> FreeBSD 10X doesn't seem to have this problem. FreeBSD11 definitely does,
> and apparently I'm not the only one who can see it. I should also point out
> that Windows VM's (both Server 2012 R2 and 7 pro - both 64bit) have no
> problem migrating to another host and then back. And FreeBSD can definitely
> migrate to another host - just not then back to the first (at least...
> immediately. I haven't tried waiting an hour or so and then trying the
> migration back).
> I also cannot select the source host as the destination in Xencenter. The
> host servers are completely identical in every respect. All vm's disk is via
> iSCSI as above.
> I also have a completely separate architecture that is identical to the
> above, except much larger, using xenserver 6.5, HP DL1000's, and cisco 3750G
> stacks. I have not yet tested freebsd11 on that installation; I assumed it
> wouldn't be much help as it's older versions of all the code.
> The smaller architecture above is not yet in production, so I can do testing
> on it. The larger installation mentioned later above is production, and I
> can't do much major testing there.

Thanks for such accurate description. I've now setup a similar environment and 
I'm able to see these glitches, as said the VM doesn't really hang, it just 
stuck for a long time (and I think that depends on the uptime differences 
between the source and destination hosts). In the meantime, could you please 
test if changing the timecounter from XENTIMER to any other (like HPET or 
ACPI-fast) solves the issue?

# sysctl -w kern.timecounter.hardware=ACPI-fast

Thanks, Roger.
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