Mar 19, 2018

What is Redis? | Why and When to use Redis?

The other day my development team's Solutions Architect came to me and asked me to deploy Ubuntu based Redis servers in our QA environment so that the developers could test using Redis for session state instead of logging to a Microsoft SQL database. This was their solution to poor performance issues in our applications. Apparently the session state transactions were causing a bottleneck in Microsoft SQL.

Anyway, I had never heard of Redis so I found this video on YouTube that explains what Redis is and why you might want to use Redis:

Also shown in the video, here is a description of what Redis is from their website:
Redis is an open source (BSD licensed), in-memory data structure store, used as a database, cache and message broker. It supports data structures such as strings, hashes, lists, sets, sorted sets with range queries, bitmaps, hyperloglogs and geospatial indexes with radius queries. Redis has built-in replication, Lua scripting, LRU eviction, transactions and different levels of on-disk persistence, and provides high availability via Redis Sentinel and automatic partitioning with Redis Cluster. 
You might be wondering how to install Redis in Ubuntu. I'm glad you asked, because Redis is available in the Ubuntu repositories, so installation is as simple as running:
  • sudo apt-get update && sudo apt-get install redis-server
Do you use Redis in your environment? If so, what are you using it for? Let us know in the comments!

Mar 16, 2018

How To Resize a Storage Repository (SR) in XenServer

The other weekend I got a disk space alert from my backup server in my Arizona data center. This happens occasionally. Since this is a VM, I usually just increase the virtual disk, then extend the drive in Windows. No big deal. Well this time, I couldn't extend the virtual drive without first increasing the size of my storage repository (SR).

Well, increasing the size of a storage repository in XenServer isn't as easy as in VMWare, but it's still not that difficult. You just have to SSH into your XenServers to do it, and it only takes 11 steps really:

  • On your SAN, extend the volume/LUN
  • SSH into your master node
  • Run xe sr-list name-label=<your SR name you want to resize>. Note the uuid of the SR.
  • Run pvscan | grep <the uuid you noted in the previous step>. Note the device name (eg: PV /dev/sdj )
  • Run echo 1 > /sys/block/device/device/rescan (e.g. echo 1 > /sys/block/sdj/device/rescan)
  • Run pvresize <device name> (eg: pvresize /dev/sdj )
  • Run xe sr-scan <the uuid you noted in step 3>
  • Verify that the XE host sees the larger physical disk by running: pvscan | grep <the uuid you noted in step 3>
  • SSH into each slave nodes
  • Run pvresize <device name> (eg: pvresize /dev/sdj )
  • Run xe sr-scan <the uuid you noted in step3>
That's it, now when you look in XenCenter, you should see that your SR has been resized accordingly.

[H/T cdillard]

Mar 15, 2018

Modern free alternative to Cliffs Notes

When I was in high school and junior high (Yes, I went to junior high and not a middle school) like just about every kid, I had to read lots of classic novels for language arts class. Well, let's be honest, I was assigned the task of reading the book, but I never did.

No, like quite a lot of kids at the time we would get our hands on Cliffs Notes, usually from the book store in the mall, and do all of our related assignments based off of the summaries from Cliffs Notes. Most of the time, it had all the answers we needed, without having to waste our time reading boring books. Is that cheating? Maybe, but I certainly didn't care.

Well the other day my daughter was given a reading assignment for a book called Hush, but the trouble was that her teacher wouldn't let her bring the book home. Because of this, she was falling behind in class. Well, in doing a little research, I found what is basically a free alternative to Cliffs Notes to help her with her assignment!

It's a site called Schmoop! Via their about page:
Since 2009, Shmoop has been a digital publishing company with a point of view. Our teaching method revolves around the basic idea that learning is often too hard—so we carry gallons of academic WD-40 to squirt on the tracks whenever we can. And as an added bonus, we're funny. At least we like to think so. 
We own 100% of our content and present both a consistent voice and a distinctive product offering. Our free Learning Guides, Online Courses, College Readiness Prep, and Test Prep balance a teen-friendly, approachable style with academically rigorous materials to help students understand why they should care. 
We also give students an honest look into life after high school. Our Careers page is written by real, studly Oil Rig Drillers, Delta Force Captains, and Marine Biologists, while our College 101 section tells students what college might actually look, feel, and smell like. Thousands of schools around the world use Shmoop as part of their curriculum, and the company has also been honored by the Interwebs: twice by the Webby Awards and twice by Scholastic Administrator Magazine ("Best in Tech"). 
By way of further Shmoopy introduction, check out our "What Is Shmoop" video (part of our fast-growing Shmoopsterpiece Theater video project) or read about us in the press!
Anyway, not only did I find summaries for my daughter's book Hush, I also searched their site and found summaries for some of the books I was supposed to read as a kid too! Books like The Great Gatsby and To Kill a Mockingbird.

Some might get on my case for not making my daughter read the book. I would have if the teacher let her bring it home, but since the teacher wouldn't, but still wanted the assignment done, I felt like this was acceptable. Besides, I'd rather encourage her to read things she's actually interested in anyway.

What do you think of this site? Would it have helped you our in high school, or junior high? Let us know in the comments!

Mar 14, 2018

Free Open Source Fork of Citrix XenServer?

The other day I wrote about where you can download older versions of Citrix XenServer since they removed a lot of features from their free version in 7.3, and then removed access to older version to force people to upgrade... Dick move right?

Well, apparently I'm not the only person pissed off by this. A whole group of developers decided to launch a new project called XCP-ng or Xen Cloud Platform Next Generation! Their goal? To provide a community driven version of Citrix's  XenServer that, unlike the original open source Xen Project, will look and feel the same as Citrix's version, along with the ease of use.... At least that's what it looks like to me.

Check out their video:

Their project page actually lists the following as their goal:
The main goal is to be able to enjoy Xenserver power (XAPI/features) with a real community backed solution (not “one company dependent”). So it should be:
  • 99.99% compatible with XenServer (as possible): ie being able to transfer VMs from XS to XCP-ng and vice-versa
  • 99.99% compatible with Open Source management solutions (like Xen Orchestra)
  • A well-documented build process, such that the product can be built by anyone from source.
  • Builds that are completely independent of any Citrix/XenServer binary (RPM) repositories.
Their initial prototype is anticipated in Q1 of 2018, which is almost over. Will they make it? Only time will tell I suppose. If they do make it, and it works well, this could prove to be the perfect alternative to Citrix's forced upgrade tactics thus far.

What do you think about this? Let us know in the comments!

Mar 13, 2018

#Bitcoin is "Crashing" Again... Why We're Not Worried

People seem to be worried again that bitcoin has started dropping.  But we are not worried, and neither should you be.  Alessio Rastani explains why.

Mar 12, 2018

Why does Google Chrome think I'm in India?

I've noticed a weird issue in Google Chrome lately, and that is whenever I type a search term in the address bar, the results come from If you didn't know, that is the URL for Google in India... I however most certainly don't live in India...

Well, after searching around I found out that quite a few others have noticed the same thing. The best solution I can find to make it stop is to do the following in Chrome:

  • Go to Settings > Manage Search Engines
  • Scroll down to the Add a new search engine box
  • Enter Google NCR for the name
  • Enter Google NCR_ for the keyword type
  • In the URL use
  • Set that as your default search provider
If you are wondering, NCR stands for No Country Redirect. This will make sure your search terms always use good old and not any other country's search!

Did this help you out? Let us know in the comments!

[H/T TheSEMPost]

Mar 9, 2018

VMs Missing in XenCenter When One or More XenServers Are Unavailable

The other night was one of those nights from hell that inevitably come up once in a while. This occasion was in one of my day job's lower tier environments where we run everything in a XenServer cluster. Well, this particular night was a power maintenance night for our data center, and two of our XenServer only had single power supplies.

Well, if you guessed that the two with single power supplies shut down, you guessed right. There were some other issues as well, that lead to this next problem, but I won't bore you with the details. You're probably here because of what happened after I finally got the other nodes back online.

What happened once I got some of my other equipment back online, and with only three out of five XenServers still running, I couldn't see any of the VMs that were originally running on the two offline nodes. Those VMs were just gone!

It turns out, they weren't gone, the cluster just thought they were still running on the two other nodes. When that happens, you have to tell the cluster to forcefully shut them down. To do that, SSH into your master node and run the following to get a list of UUID's of all the hosts in the cluster:
  • xe host-list params=uuid,name-label,host-metrics-live
Note the long UUID string of the host or hosts that are offline. Then run this command to tell the cluster that any VMs running on the offline nodes are powered off:
  • xe vm-reset-powerstate resident-on=<UUID OF OFFLINE XENSERVER> --force --multiple
Obviously replace the item in red above with the UUID of your offline XenServer, and run that command for any other offline servers as well.

Now the VMs should show up as powered off in XenCenter. You should now be able to power them on and have them run on one of the live nodes. 

Please note, when powering on one of these VMs you may get an error that says:
 the vdi is not available
I wrote about how to fix that error yesterday. To read that article, please click here: (How to fix "The VDI is not available" error in Xenserver)

Did this help you out? Did you do something different? Let us know in the comments!

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