Oh Fun!
Xen is a nice system. I have so many surprises with what I can do with it and PXE and UEFI.
I think it, and its documentation, broke my mind a little while ago though.
Shiny!!!
Countdown starts for new Xen hypervisor release
The Xen Project has issued the first release candidate for version 4.10 of its hypervisor and set a testing schedule aimed at a December release. The Project has previously foreshadowed the addition of PVHv2 for interrupt routing and PCI emulation in this release. Numerous enhancements aimed at improving the hypervisor's …
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Monday 23rd October 2017 09:22 GMT defiler
I've rarely used Xen
...Just the odd VM here and there. I did run a Citrix XenServer some time ago. Turns out that taking snapshots for backups was a bad idea. ISTR it was all LVM snapshots, but XenServer never actually removed them - just took them out of the admin console. The whole thing got slower and slower as the backup chains got longer, and it took up more and more SAN space. Eventually (I suspect after 256 snapshots), it just refused to snapshot any more.
That was the point where I finally got funds to put in VMware ESXi 4.1, so that shows you how long ago it was. I sincerely hope it's improved since then.
The Xen Hypervisor itself was pretty solid though!
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Monday 23rd October 2017 10:07 GMT TonyJ
Re: I've rarely used Xen
Snapshots at a hypervisor level have never been a backup mechanism.
Now snapshot-aware backups are of course useful, but that's not the same thing.
Must admit I have only used Xen in it's Citrix form here and there but it always felt a bit clunky by comparison to the others out there. Mind you, that could also be down to the very fact I encountered it only rarely.
Gotta ask though...hypervisors for cars??? Why? (That is a genuine question)
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Monday 23rd October 2017 12:11 GMT defiler
Re: I've rarely used Xen
Snapshots at a hypervisor level have never been a backup mechanism.
Now snapshot-aware backups are of course useful, but that's not the same thing.
How about home-rolled Perl scripts that kick off a snapshot to freeze all of the data in the middle of the night, and then extract the frozen copies of the drives to a staging JBOD before removing the snapshot and committing to tape?
Worked a treat for years in a variety of guises, covering VMware GSX, VMware Server 1, XenServer 5.5 and finally ESXi 4.1. Especially when no money was forthcoming for server software, so VCB wasn't an option. Much happier to be using Veeam these days (although I've just had an email saying they're putting their prices up...)
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Monday 23rd October 2017 21:52 GMT Eddy Ito
Hypervisors for cars
I could see where one might want to have the low priority infotainment part running in a different VM from the more critical systems especially as we tend toward more autonomy. Anything that aids to prevent a compromise of the music streaming subsystem from taking down something like the brakes or spuriously setting off an airbag at random has to be a good thing.
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Monday 23rd October 2017 12:34 GMT jms222
Hyper spaghetti
> Gotta ask though...hypervisors for cars??? Why? (That is a genuine question)
Exactly. I used to do automotive (8-bit micros, Lucas Automotive, first rolling and temporally coded remote locking). I made sure if you ran a coarse file across between the battery terminal and the terminal clamp it was supposed to connect to making lots of electronics very unhappy and things under the bonnet click our unit would still recover with the correct alarm state and let you start the car (if unlocked of course). Modern stuff is bloated enough with heavy operating systems. Why anybody would want to introduce a hypervisor, which let's face it is just operating system spaghetti, beats me.
As for backups as somebody said snapshotting at the block device level might work but isn't really satisfactory. How about ZFS or another filesystem with snapshotting built-in ?
Jon
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Monday 23rd October 2017 13:03 GMT defiler
Re: Hyper spaghetti
How about ZFS or another filesystem with snapshotting built-in ?
The problem is with applications keeping the files open / buffers needing flushed.
VMware has a button on the snapshot window to "quiesce guest filesystem", which forces it to flush the buffers, but won't write any application state out to the drives. In general you'll get away with re-running transaction logs to get databases (including Exchange Server) up-to-date. Personally I never ran into a problem with it (a bit further down the road I deployed file-level backups using Bacula which meant that those were closed, flushed and safe), but there are certainly situations where it would be a Bad Thing™.
Did I use it in the past to cover backups for several small businesses? Yes, I did. Was there ever a problem restoring files? No, there was not. Would I use it for a server handling hundreds of users? No, I wouldn't.
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Biting the hand that feeds IT
