Of course, as always, OpenStack/KVM and Docker get a lot of love, but Xen and XenServer are once again ignored. This post is my solution. With the prebuilt images distributed here and the kickstart scripts below, you can deploy Fedora 21 on your own XenServer (6.2+). Continue reading “Fedora 21 on XenServer”
When I first came to Penn, the website for the Nominations & Elections Committee looked like this:
NEC website redesign
I set out to redevelop and redesign this, upgrading it from a static HTML site edited over SFTP to a WordPress CMS on Canvas. More importantly, the website redesign in 2012 needed to fit the rebranding that Penn underwent that academic year. In other words, I wanted it to look more like the university’s design. (An email to the Communications office responsible for web assets clarified that we could, in fact, do this.)
The YYYY-MM-DD format (%Y-%m-%d) is an internationally accepted, and standardized (ISO 8601) date format. The entire ISO 8601 system is based on big-endian ordering (greatest-to-least units) within the string, so… year, month, day, hour, minute, second. It makes a hell lot more sense than the American traditional MM/DD/YY format. So much so, in fact, that ANSI and the National Institute of Standards and Technology (NIST) have both adopted it. In some countries, like China, the traditional format in the language follows the same big-endianness: 2006年1月29日, which spells out 2006-01-29.
The advantage of this format isn’t just for programmers, where sorting dates and times requires no special logic (i.e. 2014-01-31 unambiguously precedes 2014-02-01, even if they were both written without delimiter symbols).
The format also eliminates any confusion between the fields. For instance, though colloquial American 11/12/13 should be interpreted as November 12, __13, it could just as easily pass for December 13, 2011. There is no room for confusion in 2013-11-12.
XKCD says it best:
Now, it’s understandable that maybe Google needs to recognize people’s different formats of entering dates in their colloquial formats, like MM/DD/YY. But there is no excuse not to recognize the YYYY-MM-DD format.
Even more so, because the date in my screenshot, 1995-09-24, has no possible misinterpretation. To any rational human being, there’s no way to think that this is the 9th day of the 24th month (!) of 1995.
The performance differences between the two types has been studied for some time. Once upon a time, PV was undoubtedly faster, free of the overhead associated with full hardware emulation. With newer hardware features that have been supported for the last few years, PVHVM, which takes advantage of features in the processor as well as a Linux kernel that recognizes that it is operating as a virtual guest, has surpassed PV performance in most arenas.
Benchmarks have severe limitations. The statistics here are only meant to be compared relatively among themselves—between the PV and PVHVM guests running exactly the same specs and software. It would be a futile exercise to compare them against VMs running on other servers, which might have better SANs, lighter workloads, or faster CPUs and RAM. The specific test profiles in the Phoronix software are also based on outdated versions of Apache httpd and nginx, which makes them unreliable for assessing real-world performance.
Some of the relevant comparisons:
It’s worth noting that CentOS 7 with a 3.10 kernel performed poorly compared to other distributions—both Fedora 20 (kernel 3.15) and Ubuntu 14.04 (kernel 3.13) outperformed CentOS on web serving workloads (not shown). But the evidence pretty conclusively showed that PVHVM generally performed better than PV on all of the operating systems.
To that end, I’d like to offer a prebuilt CentOS 7.0.1406 image that runs in PVHVM on XenServer. You should feel free to choose between this and the PV version from my previous post, depending on your needs. (If you need to accommodate higher density on your server, you might be better off with PV. Run benchmarks yourself to decide what you should use.)
As before, you can decompress (xz -d ___.xvz.xz or use your GUI of choice) then import through XenCenter (File – Import…) or the command line (xe vm-import filename=___.xva).
This image is provided with no guarantees. Please let me know in the comments if you find an issue with it.
A PVHVM system requires no special accommodations when installing, except that UEFI and GPT are not certain to be supported. Merely select the “Other install media” option in XenCenter, and use a standard installer ISO/DVD. Do NOT use any of the CentOS or RHEL templates! Those will create PV guests.
An automated kickstart like the one used to create the image above may help you build a generic template. Hit <Tab> at the CentOS DVD menu and append a ks=__ parameter to use a kickstart script hosted at an HTTP location.