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Showing posts from June, 2015

The mystery of TCP segmentation offload bug

There are incidents that have a generic description 'TCP segmentation offload bug' that affects multiple virtualization platforms. The workaround is the same, by disabling this feature. Case one Virtualization Platform : KVM/QEMU Symptom : Periodically, guest would lose network connectivity after heavy load. Restarting the guest network doesn't fix the problem. Guest will be ok after rebooting. Reference : https://bugs.launchpad.net/ubuntu/+source/qemu-kvm/+bug/997978/comments/134 Workaround :    ethtool -K eth0 tx off sg off tso off ufo off gso off gro off lro off Case two Virtualization Platform : Xen Symptom : DomU hangs after network heavy load (@10 Mbyte/s). Reference : https://bugs.launchpad.net/ubuntu/+source/qemu-kvm/+bug/997978/comments/132 Workaround : disable offloading using ethtool ethtool --offload gso off tso off sg off gro off Case three Virtualization Platform : VMWare Symptom : 1. Page could not be displayed after VM migration t

SAP System Copy Procedures

Background My company uses SAP AG's Enterprise Resource Planning software. It as a complex system, but being developed by Germans has its advantages, for example the have many documentation in the form of SAP Notes and other stuff. One of the challenging task in using SAP's ERP is system migration and cloning. Two purposes for the migration : first, if you want to move the system to another hardware. The second, if we need a cloned system to do stuffs without compromising your original system. SAP's term for migration activity is 'System Copy' Where to start To find out steps needed to be done for system copy, you could read this slideshare-hosted SAP document here  (Best Practices : SAP System Landscape Copy). For another definitive starting point, check out SAP's wiki DOC-8324 System Copy and Migration . I noted that SAP has released Software Provisioning Manager from which we could do system copy, my previous system copy experiences has not involved

Cloud Storage Price

This post is a place where I would note prices relating to Cloud Storage. As A consumer Amazon : S3 (Simple Storage Service) : $0.03 /GB/month for first TB  (ref: https://aws.amazon.com/s3/pricing/) Glacier : $0.01 /GB/month EC2 Elastic Block Storage : SSD $0.1 /GB/month  magnetic : $0.05 /GB/month  + $0.05 /million IO Google : (ref : https://cloud.google.com/storage/pricing) Standard Storage : $0.026 /GB/month, $0.01 /GB/month nearline   Microsoft sells: (ref : https://onedrive.live.com/about/en-us/plans/) 15 GB : free 100 GB : $1.99 /month (means  $0.019 /GB/month) 200 GB : $3.99 /month 1 TB : $7 / month (include Office 365) As a provider  SwiftStack controller : (http://itknowledgeexchange.techtarget.com/storage-soup/swiftstack-enters-software-defined-storage-race/) subscription : $10 / TB/month (means $0.01 /GB/month) EMC VIPR :  (http://silvertonconsulting.com/blog/2013/09/30/emc-vipr-virtues-vexations-but-no-virtualization/#sthash.CEFmpF86