Is it your SSH client that's timing out? Or Git? Or ...?

After some time "repo sync" ( repo is the special wrapper command that actually uses git ) that is being processes stops with following error:

"error: Cannot fetch kernel/common3067733), 618.14 MiB | 2.41 MiB/s"

It happens every time I issue the command. The repository has approximately 10 GB.

Does it have to do something with droplet disk size. I am using basic droplet with 20 GB storage. Is this storage used for operating system / virtual machine ?

I am using basic droplet with 20 GB storage. Is this storage used for operating system / virtual machine ?

Yes, it is. How much space do you have free?

df -h

Filesystem Size Used Avail Use% Mounted on
/dev/vda 20G 17G 2.6G 87% /
udev 242M 4.0K 242M 1% /dev
tmpfs 99M 248K 99M 1% /run
none 5.0M 0 5.0M 0% /run/lock
none 246M 0 246M 0% /run/shm

How can I increase disk size ?

You have only 2.6GB available, you need to upgrade your droplet:

Snapshot your droplet, destroy your droplet, tcreate a new droplet from the snapsho (or Snapshot your droplet, create a new droplet from the snapshot, destroy your old droplet, if you're nervous about having no droplet for a little bit, but the first will probably preserve your ip address, but the second won't).