Październik, 2013

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ESXi cannot resolve names

poniedziałek, Październik 28th, 2013

I have recently encountered a strange problem when an updated (ESX 4.1 -> ESXi 5.1) host would not connect to the vCenter. The host would be up and respond to ping but no connection to vCenter. A usual troubleshooting step  pinging vCenter server from the host showed that the vCenter server’s name could not be resolved. Ping via IP worked fine. Checking hosts file showed that all entries were fine. Worse, the host was not able to resolve localhost either – hence problems wih starting services. So what has changed?

After the upgrade has been done, I added DNS servers to the host’s configuration. So let’s try to remove them. After I commented out the entries in resolve.conf file – bam! – everything started working again. I restarted the management services and the host connected to vCenter. But, well, I needed these DNS entries.

Finally I found out that the /etc/nsswitch.conf was completely empty. I am not sure if it was like that before. The simplest way to resolve the problem was to copy a correct file from another host, review it to make sure all settings were fine, replace it on a faulty host and reboot the server. After the reboot the server connected correctly to vCenter and all names resolution worked fine.

Transparent Page Sharing nowadays

środa, Październik 23rd, 2013

I run accross a really great article by Jason Boche that puts some light on what can gradually happen to the consolidation when newer operating systems are intruduced. It’s really eys-opening and this is something that can slip our attention as it happens gradually. It all focuses on the fact that large pages (2MB) are not considered by Transparent Page Sharing mechanism. For two reasons basically: 1) because the possibility of matching pages is much lowe and 2) because it is much more work-intensive. As a result as newer OSes are introduced and begin using large pages, the memory saved by TPS is smaller. It’s yet another case of performance vs. resurce saving. You’re the one to choose.

I really appreciated tests done by Jason to check how much memory can be saved by forcing small pages. Be sure to check out his article.

Citrix XenApp Server: Protocol Driver Error – fixed the easy way

czwartek, Październik 17th, 2013

When using Citrix Presentation Server 4.5 one day you may be welcomed with the following message when trying to open a hosted application:

Unable to launch your application. Contact your help desk with the following information: Cannot connect to the Citrix XenApp server. Protocol Driver error.

As described in Citrix KB article CTX136826 this can be fixed by recreating ICA-tcp listener in TS configuration. However, as noticed by my colleague Artur, one can make it work by simply disabling and re-enabling this listener. No need to delete and re-create it! :-) Hope that helps someone.