About Dusan Tekeljak

Dusan has over 6 years experience in Virtualization field. Currently working as Senior VMware plarform Architect at one of the biggest retail bank in Slovakia. He has background in closely related technologies including server operating systems, networking and storage. Used to be a member of VMware Center of Excellence at IBM, co-author of several Redpapers. His main scope of work consists from designing and performance optimization of business critical virtualized solutions on vSphere, including, but not limited to Oracle WebLogic, MSSQL and others. He holds several IT industry leading certifications like VCAP-DCD, VCAP-DCA, MCITP and the others. Honored with #vExpert2015 and 2016 awards by VMware for his contribution to the community. Opinions are my own!

IBM FlashSystem V9000 and VMware vSphere ESXi Guidelines

I’m really glad I had opportunity to participate on a RedBook residency regarding IBM FlashSystem V9000 and VMware “Best Practices” (it was actually one of my last thing which I did as IBMer) and till the RedPaper is released for public I decided to write a sneak peek with some … Continue reading

A new IBM SVC, Storwize (Spectrum Virtualize) v7.5 brings VVols, HyperSwap…

IBM made an announcement last week that a new IBM Spectrum Virtualize Software V7.5.0 is coming soon (5th June 2015), which will bring supports for the features like vSphere VVols, HyperSwap, Microsoft ODX… If you haven’t heard yet, IBM replaced Storwize family naming earlier this year with Spectrum Virtualize Software. … Continue reading

ALERT: VENOM Vulnerability CVE-2015-3456, Clouds Exposed!

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Crowdstrike disclosed a serious VM Escape vulnerability – codename VENOM, CVE-2015-3456 which has been around here since 2004. This one is especially serious because it is affecting the VMs in their default configuration and could be also affecting thousands of the VMs in cloud. This vulnerability may allow an attacker … Continue reading

UPDATE: New ESXi 5.5 patches called off !!!

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Apparently VMware called off latest patches for ESXi 5.5 released on 30.4.2015, However all of them can be still residing in your Update Manager! There is no official statement from VMware out there yet, but I suggest you do not apply following patches: ESX550-201504101-SG ESX550-201504101-BG ESX550-201504102-BG ESX550-201504104-BG I have found … Continue reading

IBM/Lenovo (Pure) Flex system and vSphere part1: Useless stuff

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In the last two years I was participating on the many designs, implementations and reviews of the vSphere on IBM/Lenovo Flex System or PureFlex, if you want to call like that. Therefore today I would like to share with you my preferred way of doing it right from vSphere perspective … Continue reading

Updated: Storage disconnects when using VAAI ATS on vSphere 5.5 Update2 and vSphere 6.0

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IBM has released a flash alert regarding a new behavior introduced in vSphere 5.5 Update2 and vSphere 6.0 where VAAI ATS (Atomic Test and Set or in the other words Hardware accelerated locking) is used for heartbeat I/O. http://www-01.ibm.com/support/docview.wss?uid=ssg1S1005201 According to IBM: Due to the low timeout value for heartbeat … Continue reading

Corrupted Backups using CBT

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New issue was discovered which may result in corrupted backups leveraging vSphere CBT (Change Block Tracking) for incremental backups. Basically all backup products which use VMware API for Backups ( Virtual Disk Development Kit (VDDK) )are affected. This issue occurs when you expand a virtual disk vmdk file which has … Continue reading

In Guest Disk Mirroring

If you decided to go with disk mirroring inside your guest operating system across two SAN LUNs for whatever reason (e.g. you want to bring another level of the protection for your application and your SAN environment does not support “stretch cluster” implementation, no support for synchronous mirroring, budget constrains … Continue reading

Disabling inter-VM TPS by default? How will it impact your environment?

You may be aware about recent academic research regarding potential  TPS (Transparent Page Sharing) (enabled by default) vulnerability, where you may be able to determine AES encryption key from memory timings. VMware response for this (although they do not believe it can be used in real world): they will disable … Continue reading

Manually remove ESXi host from vCenter database

Some time ago, after I tried to remove ESXi host from vCenter it was still appearing in vSphere client with alert and I couldn’t remove it again. Someone would say it is just cosmetic issue, but for example storage service was failing from initializing because of it too. VMware support … Continue reading