virtualirfan

Wow! RHEL 5 release notes for Xen

The anxiously awaited RHEL5 was released recently. The following is from RHEL5 release notes. Looks like virtualization support (with Xen 3) is only half- or perhaps only quarter-baked.

“Fully virtualized guests cannot be saved, restored or migrated.”

So, does that mean no suspend/resume and no VMotion?

“Hardware-virtualized guests cannot have more than 2GB of virtual memory.”

One really shouldn’t try putting Enterprise or even SMB workloads with only 2GB upper limit.

“When you install a fully virtualized guest configured with vcpus=2, the fully virtualized guest may take an unreasonably long time to boot up. To work around this, destroy the slow-booting guest using the command xm destroy and then use xm create to start the same guest afterwards.”

Isn’t there going to be guest filesystem corruption? Anyone know what the real bug is causing these hangs?

“When guest operating systems are configured to use sparse files, dom0 can run out of disk space. Such occurences prevent guest disk writes from completing, and can cause data loss in guests. Further, guests that use sparse files do not synchronize I/O safely. As such, it is recommended that you use non-sparse files instead. To configure guests to use non-sparse files, use the option –nonsparse when conducting a virt-install.”

Why not just make the safe option the default? Are they saying that new guests installed using default options are going to result in data loss? This implies that storage overcommitment is out the window.

rmmod xennet causes domU to crash”

fyi: I haven’t tried to test any of these limits myself but I trust these to be actually serious issues otherwise RedHat wouldn’t have posted them to the release notes.

Way long ago (in internet time) in July last year, Alex Pinchev of RedHat said:

“[Xen] is not stable yet, it’s not ready for the enterprise,… we don’t feel that [Xen] is stable enough to address banking, telco, or any other enterprise customer …”

At the time, there was a lot of hoopla about this quote. I myself wondered why a senior person at RedHat might have said this. Reading the release notes, I think I now understand what he was talking about. At least Mr. Pinchev was honest.

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