New stats in iostat

Recelnty I've noticed that iostat (for RedHat sysstat-9.0.4-31 version) reports new fields: r_await and w_await.

Following online documentation: this stands for:

The average time (in milliseconds) for I/O requests issued to the device to be served. This includes the time spent by the requests in queue and the time spent servicing them.

Munin KVM VMs real memory usage plugin

I've got some machines that use KVM as virtualization platform. I monitor then using munin, but I was not able to find munin plugin that shows proper usage of memory by virtual machines. I've found this one, but it shows memory declared for VM in config file (maximum memory value for VM to be honest). So this one is not good if you want to see realtime memory usage.

How to trace ssh tunneled/proxied connections

Almost everyone knows ssh port forward (-L/-R) or dynamic port forward (-D) features. They are very useful. For example when connecting to the internet using hotspot or other free access point it's very good idea to use ssh dynamic port forward. Doing so prevents other users from beeing able to see your traffic.

Why update to newer versions - munin

Ppl tend to not update their software. There is a rule "If something works, do not touch it". But this rule is not true.
Lately I've update munin to version 2.0.19-1, and after checking performance of my kvm nodes I got really surprised. CPU usage for host which is mostly generating munin raports dropped from 23% to about 12%, which means that new version is 2 times faster!!!
All nice cpu usage on the graph is munin.

LUKS and intel aes-ni performance part 2

Lately I've bought laptop with Intel i7-3720QM. Laptop got 2 disks: SSD Vertex 120GB and original WD Scorpio 7200rpm hdd. I have to check LUKS performance of this setup ('cause I use LUKS on daily basis). And it looks like this (of course bonnie++ results):

HT on, WD Scorpio 320GB 7200rpm, lvm, ext4, no encryption:

JBO-30003: The application pool failed ...

Lately I've been troubleshooting "JBO-30003: The application pool failed to checkout an application module" error with Oracle Application Server 10g. The person which reported the error, said that this is definitely server side issue. So I started to debug this problematic java application.

Oracle Metalink and Oracle forums claims that this is DB connection related error. So after dealing with some OC4J different configurations I started to debug this application on OS level.

Usb2 vs usb3 under linux

Lately I've been buying laptop for myself. And was wandering if I need one with usb3 ports. I've already got usb3 mobile 2'5 hdd, but I've thought that 5400rpm hdd doesn't really need usb3. Finally I've got laptop with usb3 so I have to run some tests ;).
Used bonnie++ on hdd connected to usb3 port and usb2 port. Here are results:



In quest of perfect laptop

Lately (for like 3 years), I've been looking for perfect laptop. I've been using 10+ of them during that period owned two, having three company ones. One of company laptops was almost perfect.
What is perfect laptop for me? Having those features:
* cpu with virtualization (to let me use windows VMs),
* cpu with AES (to let me use my luks crypted disks without loosing too much performance),
* gpu with vdpau support, which means nvidia card (with at least pure video feature set C),
* fast 300GB+ hdd – 7200 rpm, hybrid or ssd,

Useful shell/kernel commands

Some useful commands you can issue from shell, to change some kernel/system parameters. Guess there gonna be more later, but now some I use very often.

echo "scheduler_name" > /sys/block/"device_name"/queue/scheduler
changes ioscheduler for block device "device_name" (e.g. sda, xvda, hda), to "scheduler_name", where "scheduler_name" could be: noop, anticipatory, deadline or cfq.

To rescan SCSI device use:
echo "1" > /sys/bus/scsi/drivers/sd/"device_address"/rescan where "device_address" is something like 0:2:0:0.

Bonnie++ results database

Finally I've just found small amount of time to write 2 PHP scripts and create database with all bonnie++ results I've got. All tests were run by me. Some tests do not have character speeds (those got -1 value there). You can sort results by: block write speed, character write speed, rewrite, block read speed, character read speed and seeks. You can also narrow results down by filtering LVM, encryption and filesystem type. Every new bonnie++ runs gonna go there.

Hope some of you gonna find this useful. Link is


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by Dr. Radut