Why does my SSD not issue 1MB IO’s?

Published: (Updated: ) in SSD Performance, , , , , by . Leave a Comment on Why does my SSD not issue 1MB IO’s?.

First things First Why do we tend to use 1MB IO sizes for throughput benchmarking? To achieve the maximum throughput on a storage device, we will usually use a large IO size to maximize the amount of data is transferred per IO request. The idea is to make the ratio of data-transfers to IO requests […]

Duplicate IP issues with Linux and virtual machine cloning.

Published: (Updated: ) in Automation & Administration, , by .

TL;DR – Some modern Linux distributions use a newer method of identification which, when combined with DHCP can result in duplicate IP addresses when cloning VMs, even when the VMs have unique MAC addresses. To resolve, do the following ( remove file, run the systemd-machine-id-setup command, reboot): # rm /etc/machine-id # systemd-machine-id-setup # reboot When […]

Performance gains for postgres on Linux with hugepages

Published: (Updated: ) in Performance Tuning, , , , by .

For this experiment I am using Postgres v11 on Linux 3.10 kernel. The goal was to see what gains can be made from using hugepages. I use the “built in” benchmark pgbench to run a simple set of queries. Since I am interested in only the gains from hugepages I chose to use the “-S” […]

The return of misaligned IO

Published: (Updated: ) in Debugging, , , by .

We have started seeing misaligned partitions on Linux guests runnning certain HDFS distributions.  How these partitions became mis-aligned is a bit of a mystery, because the only way I know how to do this on Linux is to create a partition using old DOS format like this (using -c=dos  and -u=cylinders) 

Work around for bios.hddOrder when creating an OVF/OVA template.

Published: (Updated: ) in Automation & Administration, , by . Leave a Comment on Work around for bios.hddOrder when creating an OVF/OVA template..

When changing SCSI devices in an ESX based VM, it’s easy to screw up the ability to boot.  The simple fix is to add bios.hddOrder = “scsi0:0” to the end of the .vmx file.  This has always worked for me.  The problem with this solution is that any OVF/OVA that is created from the VM […]