---
layout: default
navsection: userguide
title: "Storing and Retrieving data using Keep"
...
This tutorial introduces you to the Arvados file storage system.
*This tutorial assumes that you are "logged into an Arvados VM instance":{{site.baseurl}}/user/getting_started/ssh-access.html#login, and have a "working environment.":{{site.baseurl}}/user/getting_started/check-environment.html*
The Arvados distributed file system is called *Keep*. Keep is a content-addressable file system. This means that files are managed using special unique identifiers derived from the _contents_ of the file, rather than human-assigned file names (specifically, the MD5 hash). This has a number of advantages:
* Files can be stored and replicated across a cluster of servers without requiring a central name server.
* Both the server and client systematically validate data integrity because the checksum is built into the identifier.
* Data duplication is minimized—two files with the same contents will have in the same identifier, and will not be stored twice.
* It avoids data race conditions, since an identifier always points to the same data.
h1. Putting Data into Keep
We will start by downloading a freely available VCF file from "Personal Genome Project (PGP)":http://www.personalgenomes.org subject "hu599905":https://my.personalgenomes.org/profile/hu599905 to a staging directory on the VM, and adding it to Keep. In the following commands, replace *@you@* with your login name.
First, log into your Arvados VM and set up the staging area:
notextile. <pre><code>~$ <span class="userinput">mkdir /scratch/<b>you</b></span></code></pre>
Next, download the file:
<notextile>
<pre><code>~$ <span class="userinput">cd /scratch/<b>you</b></span>
/scratch/<b>you</b>$ <span class="userinput">curl -o var-GS000016015-ASM.tsv.bz2 'https://warehouse.personalgenomes.org/warehouse/f815ec01d5d2f11cb12874ab2ed50daa+234+K@ant/var-GS000016015-ASM.tsv.bz2'</span>
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 216M 100 216M 0 0 10.0M 0 0:00:21 0:00:21 --:--:-- 9361k
</code></pre>
</notextile>
{% include 'notebox_begin' %}
If you have your own data, for example @MyData.vcf@, you can use @scp@ or @rsync@ to copy from your local workstation to the shell VM (run this on your local workstation):
notextile. <pre><code>~$ <span class="userinput">scp MyData.vcf <b>you@shell</b>.arvados:/scratch/<b>you</b>/MyData.vcf</span></code></pre>
{% include 'notebox_end' %}
Now use @arv keep put@ to add your VCF data to Keep, then delete the local copy of the file:
<notextile>
<pre><code>/scratch/<b>you</b>$ <span class="userinput">arv keep put var-GS000016015-ASM.tsv.bz2</span>
c1bad4b39ca5a924e481008009d94e32+210
/scratch/<b>you</b>$ <span class="userinput">rm var-GS000016015-ASM.tsv.bz2</span>
</code></pre>
</notextile>
The output value @c1bad4b39ca5a924e481008009d94e32+210@ from @arv keep put@ is the Keep locator. This enables you to access the file you just uploaded, and is explained in the next section.
h2(#dir). Putting a directory
You can also use @arv keep put@ to add an entire directory:
<notextile>
<pre><code>/scratch/<b>you</b>$ <span class="userinput">mkdir tmp</span>
/scratch/<b>you</b>$ <span class="userinput">echo "hello alice" > tmp/alice.txt</span>
/scratch/<b>you</b>$ <span class="userinput">echo "hello bob" > tmp/bob.txt</span>
/scratch/<b>you</b>$ <span class="userinput">echo "hello carol" > tmp/carol.txt</span>
/scratch/<b>you</b>$ <span class="userinput">arv keep put tmp</span>
0M / 0M 100.0%
887cd41e9c613463eab2f0d885c6dd96+83
</code></pre>
</notextile>
The locator @887cd41e9c613463eab2f0d885c6dd96+83@ represents a collection with multiple files.
h1. Getting Data from Keep
h2. Using Workbench
You may access collections through the "Collections section of Arvados Workbench":https://{{ site.arvados_workbench_host }}/collections at *Data* %(rarr)→% *Collections (data files)*. You can also access individual files within a collection. Some examples:
* "https://{{ site.arvados_workbench_host }}/collections/c1bad4b39ca5a924e481008009d94e32+210":https://{{ site.arvados_workbench_host }}/collections/c1bad4b39ca5a924e481008009d94e32+210
* "https://{{ site.arvados_workbench_host }}/collections/887cd41e9c613463eab2f0d885c6dd96+83/alice.txt":https://{{ site.arvados_workbench_host }}/collections/887cd41e9c613463eab2f0d885c6dd96+83/alice.txt
h2(#arv-get). Using the command line
You can view the contents of a collection using @arv keep ls@:
<notextile>
<pre><code>/scratch/<b>you</b>$ <span class="userinput">arv keep ls c1bad4b39ca5a924e481008009d94e32+210</span>
var-GS000016015-ASM.tsv.bz2
</code></pre>
<pre><code>/scratch/<b>you</b>$ <span class="userinput">arv keep ls 887cd41e9c613463eab2f0d885c6dd96+83</span>
alice.txt
bob.txt
carol.txt
</code></pre>
</notextile>
Use @-s@ to print file sizes rounded up to the nearest kilobyte:
<notextile>
<pre><code>/scratch/<b>you</b>$ <span class="userinput">arv keep ls -s c1bad4b39ca5a924e481008009d94e32+210</span>
221887 var-GS000016015-ASM.tsv.bz2
</code></pre>
</notextile>
Use @arv keep get@ to download the contents of a collection and place it in the directory specified in the second argument (in this example, @.@ for the current directory):
<notextile>
<pre><code>/scratch/<b>you</b>$ <span class="userinput">arv keep get c1bad4b39ca5a924e481008009d94e32+210/ .</span>
/scratch/<b>you</b>$ <span class="userinput">ls var-GS000016015-ASM.tsv.bz2</span>
var-GS000016015-ASM.tsv.bz2
</code></pre>
</notextile>
You can also download individual files:
<notextile>
<pre><code>/scratch/<b>you</b>$ <span class="userinput">arv keep get 887cd41e9c613463eab2f0d885c6dd96+83/alice.txt .</span>
</code></pre>
</notextile>
With a local copy of the file, we can do some computation, for example computing the MD5 hash of the complete file:
<notextile>
<pre><code>/scratch/<b>you</b>$ <span class="userinput">md5sum var-GS000016015-ASM.tsv.bz2</span>
44b8ae3fde7a8a88d2f7ebd237625b4f var-GS000016015-ASM.tsv.bz2
</code></pre>
</notextile>
h2. Using arv-mount
Use @arv-mount@ to mount a Keep collection and access it using traditional filesystem tools.
<notextile>
<pre><code>/scratch/<b>you</b>$ <span class="userinput">mkdir -p mnt</span>
/scratch/<b>you</b>$ <span class="userinput">arv-mount --collection c1bad4b39ca5a924e481008009d94e32+210 mnt &</span>
/scratch/<b>you</b>$ <span class="userinput">cd mnt</span>
/scratch/<b>you</b>/mnt$ <span class="userinput">ls</span>
var-GS000016015-ASM.tsv.bz2
/scratch/<b>you</b>/mnt$ <span class="userinput">md5sum var-GS000016015-ASM.tsv.bz2</span>
44b8ae3fde7a8a88d2f7ebd237625b4f var-GS000016015-ASM.tsv.bz2
/scratch/<b>you</b>/mnt$ <span class="userinput">cd ..</span>
/scratch/<b>you</b>$ <span class="userinput">fusermount -u mnt</span>
</code></pre>
</notextile>
You can also mount the entire Keep namespace in "magic directory" mode:
<notextile>
<pre><code>/scratch/<b>you</b>$ <span class="userinput">mkdir -p mnt</span>
/scratch/<b>you</b>$ <span class="userinput">arv-mount mnt &</span>
/scratch/<b>you</b>$ <span class="userinput">cd mnt/c1bad4b39ca5a924e481008009d94e32+210</span>
/scratch/<b>you</b>/mnt/c1bad4b39ca5a924e481008009d94e32+210$ <span class="userinput">ls</span>
var-GS000016015-ASM.tsv.bz2
/scratch/<b>you</b>/mnt/c1bad4b39ca5a924e481008009d94e32+210$ <span class="userinput">md5sum var-GS000016015-ASM.tsv.bz2</span>
44b8ae3fde7a8a88d2f7ebd237625b4f var-GS000016015-ASM.tsv.bz2
/scratch/<b>you</b>/mnt/c1bad4b39ca5a924e481008009d94e32+210$ <span class="userinput">cd ../..</span>
/scratch/<b>you</b>$ <span class="userinput">fusermount -u mnt</span>
</code></pre>
</notextile>
@arv-mount@ provides several features:
* You can browse, open and read Keep entries as if they are regular files.
* It is easy for existing tools to access files in Keep.
* Data is downloaded on demand. It is not necessary to download an entire file or collection to start processing.