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Wednesday, August 13, 2008

Swap - VMware effects and parallelization

VMare and swap

To present our software marketing and scientific represents use Windows laptopts with Linux in VMWare. They need Linux because our web based product (Relibase+, IsoStar and incoming WebCSD) working only on it. Using virtualization shouldn't be a problem as a machine has 2GB of memory and we can assign 1GB to guest OS. However, recently we couldn't start WebCSD, not only guest was affected but also host froze. VMWare has problem with I/O operation so we were suspicious about disk usage, but the server didn't need to much of it. Anyway I went I/O trace and decided to turn off the swap. After that server started to work as a rocket!

Parallelization of a swap partitions

I was browins through IBM developersWorks and found info that you can parallelize a swap partition.

Amazingly, all modern Linux kernels, by default (with no special kernel options or patches) allow you to parallelize swap, just like a RAID 0 stripe. By using the pri option in /etc/fstab to set multiple swap partitions to the same priority, we tell Linux to use them in parallel:

/dev/sda2 none swap sw,pri=3 0 0
/dev/sdb2 none swap sw,pri=3 0 0
/dev/sdc2 none swap sw,pri=3 0 0
/dev/sdd2 none swap sw,pri=1 0 0
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