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diff --git a/website/src/learning/advanced-virt-df/index.html b/website/src/learning/advanced-virt-df/index.html new file mode 100644 index 0000000..c8840f0 --- /dev/null +++ b/website/src/learning/advanced-virt-df/index.html @@ -0,0 +1,193 @@ +[% topdir = "../.." -%] +[% PROCESS globals -%] +[% WRAPPER page + title = "Advanced use of virt-df" + h1 = "Advanced use of virt-df" + section = "learning" +%] + +<p> +This tutorial discusses advanced use of +<a href="http://www.libguestfs.org/virt-df.1.html">virt-df</a>. +Some of the topics covered are: +</p> + +<ul> +<li> Using CSV output to import data into spreadsheets, databases + and monitoring tools. </li> +<li> Graphing and using trends to predict future disk usage of guests. </li> +<li> Generating alerts when virtual machines are near to running + out of disk space. </li> +<li> Using virt-df safely with untrusted and malicious guests. </li> +</ul> + +[% WRAPPER h2 h2="CSV output" anchor="csv" %] + +<p> +If you are going to do anything apart from looking at the output of +virt-df, you should use the <code>--csv</code> flag so that virt-df +produces machine-readable +<a href="http://en.wikipedia.org/wiki/Comma-separated_Values">comma-separated +values (CSV)</a> output. The output looks like this: +</p> + +<pre> +# <b>virt-df --csv</b> +Virtual Machine,Filesystem,1K-blocks,Used,Available,Use% +"CentOS5x64","/dev/sda1",101086,19290,76577,19.1% +"CentOS5x64","/dev/VolGroup00/LogVol00",8030648,3116144,4499992,38.8% +<i>[etc]</i> +</pre> + +[% END %] + +[% WRAPPER h2 h2="Using cron" anchor="cron" %] + +<p> +You can write a cron job to collect virt-df output periodically +(I collect it once a day). +</p> + +<pre> +# <b>cat > /etc/cron.daily/local-virt-df</b> +#!/bin/bash - +date=$(date +%F) +virt-df --csv > /var/local/virt-df.$date +# <b>chmod 0755 /etc/cron.daily/local-virt-df</b> +</pre> + +<p> +The cron job will create one file every day in <code>/var/local</code>. +</p> + +[% END %] + +[% WRAPPER h2 + h2="Importing the data into spreadsheets and databases" anchor="import" %] + +<p> +CSV files can be loaded directly into spreadsheets and databases: +</p> + +<p> +<img src="df-openoffice.png" width="721" height="642" + longdesc="Screenshot showing virt-df output in OpenOffice Calc"/> +</p> + +<pre> +<b>CREATE TABLE df_data ( + "Virtual Machine" TEXT NOT NULL, + "Filesystem" TEXT NOT NULL, + "1K-blocks" BIGINT NOT NULL, + "Used" BIGINT NOT NULL, + "Available" BIGINT NOT NULL, + "Use%" TEXT +);</b> +<b>COPY df_data FROM 'df.csv' WITH DELIMITER ',' CSV HEADER;</b> +</pre> + +[% END %] + +[% WRAPPER h2 h2="Sorting and querying the data" anchor="query" %] + +<p> +Once your data has been imported, you can start to process it, +for example finding out which virtual machines are running +out of space: +</p> + +<p> +<img src="df-openoffice-sorted.png" width="653" height="143" + longdesc="Screenshot showing virt-df output in OpenOffice Calc"/> +</p> + +<p> +The following PostgreSQL query on the previously imported data +shows all filesystems with over 60% usage: +</p> + +<pre> +<b>SELECT "Virtual Machine", "Filesystem" + FROM df_data + WHERE (100. * "Used" / "1K-blocks") > 60;</b> + + Virtual Machine | Filesystem +-----------------+-------------------------------------- + Debian5x64 | /dev/debian5x64.home.annexia.org/usr + OpenSUSE11x64 | /dev/sda2 + VBox | /dev/vg_f13x64/lv_root +(3 rows) +</pre> + +[% END %] + +[% WRAPPER h2 h2="Graphs and trends" anchor="graphs" %] + +<p> +You can use daily historical data to graph disk usage. +In theory at least you could use trends in this data +to predict future requirements, although in my experience +usage tends to be <q>lumpy</q> — installing OpenOffice +in a VM results in a big increase in usage which is not +indicative of any trend. +</p> + +<p> +In any case, here is a graph of usage data for one VM filesystem +over approximately one month, generated using OpenOffice Calc +(Insert → Chart) with a linear trend line +(select chart and do Insert → Trend Lines): +</p> + +<p> +<img src="df-centos-graph.png" width="583" height="340" + longdesc="Output of virt-df for one VM graphed over one month" /> +</p> + +[% END %] + +[% WRAPPER h2 h2="Alerts" anchor="alerts" %] + + + + + + + + + +[% END %] + +[% WRAPPER h2 h2="Safety" anchor="safety" %] + +<p> +virt-df is generally safe to use with untrusted or malicious guests, +but there are some things to be aware of. +</p> + +<p> +An untrusted guest can present any disk data that it wants +to the host. By simple manipulations of the filesystem it can show +the disk as full when it is empty, or empty when it is full. This +is not important in itself, it only becomes an issue if a guest +could manipulate the statistics of another unrelated VM. +</p> + +<p> +Older versions of virt-df ran a separate libguestfs appliance for each +guest. This is safe because one guest cannot possibly interfere with +the statistics from another, but also slow. Since virt-df 1.5.0, +several unrelated guests may share a single libguestfs appliance, +which is much faster but there is a (slim) possibility that one guest +might corrupt the appliance leading to misreported statistics for +another guest. +</p> + +<p> +You can get the old, safest possible behaviour by adding +the <code>--one-per-guest</code> flag to the virt-df command line. +</p> + +[% END %] + +[% END -%] |