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Virtualization Is Not All Roses
An anonymous reader writes "Vendors and magazines are all over virtualization like a rash, like it is the Saviour for IT-kind. Not always, writes analyst Andi Mann in Computerworld." I've found that when it works, it's really cool, but it does add a layer of complexity that wasn't there before. Then again, having a disk image be a 'machine' is amazingly useful sometimes.
Yes - we have quite a bit that we just put in here at my shop.
Virtualization good: Webservers, middle tier stuff, etc.
Virtualization bad: DBs, memory intensive, CPU intensive.
Biggest issue? "Surprise" systems. You might see a system and notice a "reasonable" load average, then find out once it's on a VM that it was a really horrible candidate because it has huge memory, disk, CPU, or network spikes. VMWare especially seems to hate disk spikes.
What we learned is it's the not the average as much as the high-water-marks that really matter. A system that's quiet 99.99% of the time, but spikes to 100% for 60 seconds here or there can be nasty.
An operating system should be like a light switch... simple, effective, easy to use, and designed for everyone.
It is great for replacing things like DNS servers that are mostly CPU. However, don't try running two busy database machines on the same disk - you can't divide it up nearly as well as CPU or bandwidth use.
Also, make sure to try OpenVZ before you try Xen. If you are virtualizing all Linux machines, then VZ is IMO a better choice.
First time I've ever posted anon...
A vendor just convinced management to move all of our webhosting stuff over to a Xen virtualized environment (we're a development firm that hosts out clients) a few weeks before I hired in. No one here understands how its configured or how it works and this is the first implementation that this vendor has performed, but management believes that they walk on water. No other tech shops in the area have even the slightest bit of expertise with it. So guess what now? Come hell or high water, we can't afford to drop these guys no matter how bad they might screw up.
Who ever claims that open-source is the panacea to vendor lock-in is smoking crack. Open source gives companies enough "free" rope to hang themselves with if it isn't implemented smartly. Virtualiztion is no different.
I'm certified for both VMware ESX 2.5 and VMware VI3. VMware's best practices are to never use a single path, whether it be for NIC or FC HBA (storage). VMware also has Virtual Switches, which not only allows you to team NICs for load balancing and failover, but also use port groups (VLANs). You can then view pretty throughput graphs for either physical NICs or virtual adapters. It's crazy amazing(TM).
.5 seconds compared to an IBM xSeries 3850 which takes 6 minutes). Oh, and there is the whole snapshotting feature, memory and disk, which allows for point in time recovery on any host. Yea... downsides indeed.
As for "putting many workloads on a box and uptime," this writer should really take a look at VMware VI3 and Vmotion. Not only can you migrate a running VM without downtime, you can "enter maintenance mode" on a physical host, and using DRS (distributed resource scheduler) it will automatically migrate the VMs to hosts and achieve a load balance between CPU/Memory. It's crazy amazing(TM).
Lastly, just to toot a bit of the virtualization horn... VMware's HA will automatically restart your VMs on other physical hosts in your HA cluster. It's not unusual for a Win2k3 VM to boot in under 20 seconds (VMware's BIOS posts in about
Virtualization is Sysadmin Utopia. -- cvl, a Virtualization Consultant
From what I have seen and experienced the VM video card is the issue. The virtual machine uses the virtual hardware drivers so the actual hardware is largely irrelevant so long as the host OS can handle it. In a desparate attempt to get FFXI installed on my linux machine I resorted to attempting to use VMware only to find out that VMware does not support any kind of 3d accel stuff (again, virtual hardware vs real hardware).
The only change I can believe in is what I find in my couch cushions.
"Modern processors are way overkill for most things they're being used for."
Right - except like I said - watch those spikes. We took a system that according to our monitoring sat at essentially 0-1% used (load average: 0.01, 0.02, 0.01) and put it on a virtual. Great idea, right?
Except for the fact that once a day it runs a report that seems fairly harmless but caused the filesystem to go Read Only due to a VMWare bug. The report lasts only about 2 minutes, but it hammers the disk in apparently just the right way.
It's the spikes you have to be careful of. Just look for your high-water-marks. If the box spikes to 90% or 100% (though the load average doesn't reflect it) it will have some issues.
An operating system should be like a light switch... simple, effective, easy to use, and designed for everyone.
Your bug comment is kinda moot - it's not a normal problem with virtualization.
We have over 120 VM's running on seven hosts with VI3. Most of them, as you can imagine, are not high work-load (although we do have four Terminal Servers handling about 300 terminals total) but sometimes they are, and we've really not had any issues.
It depends on what you're doing, really. Saying you WILL have problems is any situation isn't really valid.
- It's not the Macs I hate. It's Digg users. -
That's obviously just an example - uptime doesn't provide high-water marks, etc
:D
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Ahh, slashdot. People just *love* to split hairs
Ok, last time I'm saying this:
BE CAREFUL. Not every system is an ideal candidate for virtualization, and even the ones that seem perfect at first glance can fail. Don't rely on only "overview" metrics. Do thorough inspection, and make sure you load test.
VMs rule, but there are gotchas and bugs that can be showstoppers. Just cause someone else has 300 servers running via virtualization doesn't mean you can
An operating system should be like a light switch... simple, effective, easy to use, and designed for everyone.
We took a system that according to our monitoring sat at essentially 0-1% used (load average: 0.01, 0.02, 0.01) and put it on a virtual.
Load average is a bad way of looking at machine utilization. Load average is the average number of processes on the run queue over the last 1,5,15 minutes. Programs running exclusively I/O will be on the sleep queue while the kernel does i/o stuff, giving you a load average of near-zero even though your machine is busy scrambling for files on disk or waiting for network data. Likewise, a program that consists entirely of NOOPs will give you a load average of one (+1 per each additional instance) even if its nice value is all the way up and it is quite interruptable/is really putting zero strain on your system.
Before deciding that a machine is virtualizable, don't just look at load average. Run a real monitoring utility and look at iowait times, etc.
Reid
The Right Reverend K. Reid Wightman,