Snapshots are taken per node using the nodetool snapshot command. To take a global snapshot, run the nodetool snapshot command using a parallel ssh utility, such as pssh. A snapshot first flushes all in-memory writes to disk, then makes a hard link of the SSTable files for each keyspace. You must have enough free disk space on the node to accommodate making snapshots of your data files. A single snapshot requires little disk space. However, snapshots can cause your disk usage to grow more quickly over time because a snapshot prevents old obsolete data files from being deleted. After the snapshot is complete, you can move the backup files to another location if needed, or you can leave them in place. Note: Cassandra can only restore data from a snapshot when the table schema exists. It is recommended that you also backup the schema.

Procedure

Run the nodetool snapshot command, specifying the hostname, JMX port, and keyspace. For example: $ nodetool -h localhost -p 7199 snapshot mykeyspace

Results The snapshot is created in data_directory_location / keyspace_name / table_name – UUID /snapshots/ snapshot_name directory. Each snapshot directory contains numerous .db files that contain the data at the time of the snapshot. For example: Package installations: / var /lib/cassandra/data /mykeyspace/users- 081 a1500136111e482d09318a3b15cc2/snapshots/ 1406227071618 /mykeyspace-users-ka- 1 -Data.db Tarball installations: install_location /data/data/mykeyspace/users-081a1500136111e482d09318a3b15cc2/snapshots/1406227071618/mykeyspace-users-ka-1-Data.db Taking a Global Snapshot: As stated earlier, global snapshot can be taken using the pssh tool. So let us configure this tool first, Steps for configuring the pssh are: Install the pssh tool using the following command sudo apt-get install python-pip sudo pip install pssh Create a hosts file that contains all the ip’s of the nodes present in that cluster and name it something like pssh-hosts It should look something like this : 192.168.2.123 192.168.2.125 192.168.2.120 Now run the following command so that the snapshots get created on each and every node : pssh -h pssh-hosts -P "/root/cassandra/bin/nodetool -h localhost -p 7199 snapshot "

Now youv’e taken the dump of data on each node which is present on each node, you can dowload it using secure copy and then restore it accordingly.

I am still working on automating the process of downloading the dump ! Will update you all as soon as it is done !

I hope youve enjoyed the blog !

If youv’e any query ping me here or on twitter :shiv4nsh !

Will be Happy to help you out !

Till then enjoy someone’s else’s blog ! 😉

Refrences: