Computing desk
< August 6	<< Jul \| August \| Sep >>	August 8 >

Welcome to the Wikipedia Computing Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

August 7[edit]

Nested Virtualization[edit]

Hi.

I'm wondering whether it is possible to run Virtual Machines inside another Virtual Machine, i.e. is it possible to install and run a hypervisor (such as Hyper-V, Xen, etc.) inside a Virtual Machine in order to further virtualize that Virtual Machine's hardware (which is itself of course virtualized)? This is purely a theoretical question for personal interest.

Rocketshiporion Monday 07-August-2010, 10:30am (GMT)

Yes, that is possible. IIRC, you can run VMware ESXi inside VMware Workstation (assuming the host system fulfills the requirements to run ESXi natively - i.e. 64-bit CPU, 64-bit host OS, and at least 2 GB RAM available for the guest), and I believe I saw a screenshot somewhere of VMware running inside a VirtualBox. Some combinations are blocked by the manufacturer, though. For example, you cannot run VMware Server on a Linux host that is actually a guest inside a VMware Workstation installation - you can install the software, but it will refuse to run in an already virtualized environment. -- 78.43.71.155 (talk) 11:11, 7 August 2010 (UTC)[reply]

Virtual machines cannot normally be nested using the same hypervisor: for example, you can't run Citrix on both the physical host machine and on virtual machines hosted on the physical host machine. So you would need two different hypervisors, so that you could alternate them between nesting levels, in order to avoid this problem. I think the only exception to this is Microsoft's Hyper-V, which permits direct nesting up to eight levels. Note though that Microsoft's Hyper-V is only available in their Windows Server 2008 operating-systems, and none of those are particularly cheap. A particularly good hypervisor is Xen Hypervisor. But why do want to nest virtual machines? It's a lot easier and less complicated to just keep all of the virtual machines at the root of the physical host machine, unless of course you're running one of those Microsoft hypervisor operating systems which limit the number of virtual machines you're allowed to run on your physical host machine to either one or four virtual machines. Elspetheastman (talk) 13:01, 7 August 2010 (UTC)[reply]

<squeeze>Nesting hypervisors can make sense if you want to try out a large-scale deployment without having sufficient test hardware, and don't want to run your experiments on your production hardware. So you could fire up VMware Workstation on a Windows 7 (or possibly W2K8, not sure if Workstation will install on that) 64-Bit edition or a recent 64-Bit Linux with sufficient RAM and disk space, run one or two instances of ESXi, and a couple of virtual servers simulating your production environment, then move them one by one to the ESXi instances to see if everything works as planned. -- 78.43.71.155 (talk) 13:45, 7 August 2010 (UTC)</squeeze>[reply]

I stated in my original post that "this is purely a theoretical question for personal interest"; and I'm not actually intending to nest any virtual machines. In addition, Microsoft's Hyper-V hypervisor is available separately from Windows Server 2008, as a standalone hypervisor named Microsoft Hyper-V Server 2008 R2, which is available for download completely free-of-charge. Rocketshiporion Monday 7-August-2010, 1:10pm (GMT)

Yes, Microsoft Hyper-V Server 2008 R2 is provided for free, but it's useless on its own - you need Microsoft System Center Virtual Machine Manager in order to manage any virtual machines which you host on a server running Microsoft Hyper-V Server 2008 R2, and Microsoft System Center Virtual Machine Manager is not free - in fact, its licensing model is too complicated for most people (myself included) to figure out. Elspetheastman (talk) 13:18, 7 August 2010 (UTC)[reply]

Microsoft Hyper-V Server 2008 R2, which is available as a free download, can be managed remotely from any computer running on Windows 7 by using Windows 7 Remote Server Administration Tools, which is also available as a free download. The hyperlink which you have provided for Xen Hypervisor does not lead to any webpage, but instead causes a dialog box to appear asking whether I would like to save an .iso image named livecd-xen-3.2-0.8.2-amd64.iso located at the URL http://www.xen.org/download/LiveCD/livecd-xen-3.2-0.8.2-amd64.iso to my computer. Rocketshiporion Monday 7-August-2010, 1:30pm (GMT)

RAID 6+5[edit]

Hi.

I am curious about whether a RAID span of the form RAID 6+5 exists. By RAID 6+5, I mean a single-parity span of dual-parity arrays, in which the capacity of the span conforms to the following equation.

t = (m-1)*(n-2)*d, where:

m = number of arrays in span
n = number of disks per array
t = total capacity of span
d = individual capacity of each disk

This is a theoretical question for personal interest. Rocketshiporion

Copying External Hard Disk Drives in OS X[edit]

Are there any system tools in OS X for duplicating external hard disks? —Preceding unsigned comment added by 188.220.46.47 (talk) 16:36, 7 August 2010 (UTC)[reply]

Do you mean disk cloning, or something like RAID striping? --Mr.98 (talk) 18:09, 7 August 2010 (UTC)[reply]

Disk cloning —Preceding unsigned comment added by 188.220.46.47 (talk) 21:07, 7 August 2010 (UTC)[reply]

Disk Utility can make and burn disk images (you'd make an image of one disk, then burn it to the other). I've used GParted to good effect with OS X drives, after putting it on a bootable disk. There are proprietary tools for managing disk cloning more regularly (like CopyCatX or SuperDuper), but I haven't used them, personally. I think I used CarbonCopyCloner once to good effect. It kind of depends exactly what you want it for — if it's for a one-time sort of thing, it might be easier to use something like GParted or even Disk Utility. If it is for regular backups, one of the ones that works more straightforwardly with the Mac GUI might be more sensible. --Mr.98 (talk) 21:18, 7 August 2010 (UTC)[reply]

Thanks. I was thinking of something more along the lines of a unix utility that's built in to OS X. —Preceding unsigned comment added by 188.220.46.47 (talk) 21:44, 7 August 2010 (UTC)[reply]

How about dd (Unix) ? Unilynx (talk) 22:12, 7 August 2010 (UTC)[reply]

I think you're looking for the hdiutil command (see its man page at Apple Developer). The create verb has an option for using a source folder or volume. This will not be a strict clove (files will probably be defragged like a normal copy, for instance). You might also check out the diskutil command, though that seems less appropriate. --Ludwigs2 20:43, 8 August 2010 (UTC)[reply]

Actually, the preferred CLI cloning tool is asr (e.g. "sudo asr restore --source /Volumes/SourceVol --target /Volumes/TargetVol --erase"). -- Speaker to Lampposts (talk) 04:53, 11 August 2010 (UTC)[reply]

Computers infected with malicious software/files[edit]

Would there be any way to measure this or would it just be too difficult? Have there ever been any estimates as to how many computers in the world that are infected? Chevy monte carlo 19:27, 7 August 2010 (UTC)[reply]

Here is an interesting compilation from trend micro on what they've monitored; some statistical analysis could reveal more accurate world-wide numbers. Also here is another and another. --rocketrye12^{talk/contribs} 20:29, 7 August 2010 (UTC)[reply]

Excellent finds. Thanks a lot. Chevy monte carlo 21:55, 7 August 2010 (UTC)[reply]

Define "infected", it's a very relative term in these days of marketing. Last software I saw claimed to be a Sony CD, but it actually was a rootkit. 68.71.3.254 (talk) 12:40, 12 August 2010 (UTC)[reply]

Wikipedia animation thumbnail inconsistency[edit]

How come the thumbnail of first animation in the gallery here: Front crawl#Ergonomics is animated, while the thumbnails for the second and third are not? --71.141.115.116 (talk) 21:41, 7 August 2010 (UTC)[reply]

There is likely to be a problem with the other two, as they appear to be supposed to be moving. It might be the result of an error caused by a previous editor who was trying to improve the article, or there's the less likely reason that the other two are not supposed to move. Chevy monte carlo 21:57, 7 August 2010 (UTC)[reply]

Most likely the mediawiki software didn't thumbnail the gifs properly. There might be a way to purge the cache and force a rethumbnailing. 82.43.88.151 (talk) 10:51, 8 August 2010 (UTC)[reply]

I've noticed that in general, over the last few months most animated GIFs no longer thumbnail correctly on Wikipedia. --Mr.98 (talk) 15:04, 8 August 2010 (UTC)[reply]

It is size related. Thumbnailed animated large GIFs no longer animate. The intent is apparently that "somebody" is going to go through and change them all to be in a video format. Here is a Village Pump Technical thread in which I complained about this and got some informational links about why the decision was reached and a workaround or two. Comet Tuttle (talk) 17:12, 8 August 2010 (UTC)[reply]

What's funny is that sometimes it seems to go just fine as a thumbnail. See at right. Maybe it is a cache thing with 120px image in that case. Personally I would prefer some kind of Javascript solution rather than a conversion to a "movie" format, which adds huge overhead and difficulty of reuse. --Mr.98 (talk) 00:09, 9 August 2010 (UTC)[reply]

And the "movie" format doesn't appear to be able to loop either, which is very important for many gifs 82.43.88.151 (talk) 08:23, 9 August 2010 (UTC)[reply]

Eh? [1] [2] Nil Einne (talk) 12:32, 9 August 2010 (UTC)[reply]

But HTML5 is still years away. AJ Cham 12:46, 9 August 2010 (UTC)[reply]

Actually HTML5 video can be used by wikimedia projects for video right now (with the Theora codec) and has been for at least 5 months [3]. It is supported by Firefox, Chrome and Theora. I'm pretty sure the plan is to roll this out in a form that will work for browsers which support HTML5 video and the right codec and gracefully fallback probably with a JS player for browsers that don't similar to the way video is currently implemented. And while I don't know if they have a timeline I'm pretty sure it isn't 'years away'.

Safari of course including the iPhone and iPod also supports HTML5 video but not Theora, the later 2 being somewhat famous for their lack of Flash and view of the CEO of the company that makes them that HTML5 is the future. Internet Explorer 9 beta supports HTML5 video as will I'm pretty sure the final release although like Safari I don't think Theora. Youtube and other video sites are moving or already support HTML5 video in addition to Flash although usually using H264 or WebM not Theora.

The fact that finalisation of HTML5 is years away is therefore largely irrelevant as the article you've linked to notes.

BTW, while I'm not a webdesigner, I'm pretty sure in a similar vein sites are already using elements of CSS3 even if it to has not yet been finalised.

Nil Einne (talk) 18:30, 9 August 2010 (UTC)[reply]