Frontend-storage relationship

A frontend is a single machine intended for user logins and ligh pre- and post-processing of data.

A storage is a large disc array where user data (user home directories) are kept.

As there is not one huge storage, but several large and loosely interconnected storages, users have access to several different home directories.

Every frontend has a /home directory mounted to one of the storages, e.g. /home of frontend skirit.metacentrum.cz is mounted on /storage/brno2/home, so when an user is logged on skirit, the commands ls ~ and ls /storage/brno2/home/user123 are equivalent.

A frontend has a native home directory on one, and only one, storage; however this is not true the other way round: a home directory on a certain storage may be mounted by more than one frontend:

user123@user123-XPS-13-9370:~$ ssh nympha.zcu.cz 
...
(BULLSEYE)user123@nympha:~$ pwd
/storage/plzen1/home/user123   # "plzen1" is native storage for "nympha" frontend
(BULLSEYE)user123@nympha:~$ exit 
user123@user123-XPS-13-9370:~$ ssh minos.zcu.cz
...
(BULLSEYE)user123@minos:~$ pwd
/storage/plzen1/home/user123   # "plzen1" is native storage also for "minos" frontend

The overall schema can be summed up as shown below:

Transition between storages is possible no matter which frontend an user is logged to. To get to a certain home directory, user does not need to log on a specific frontend. Users can change their home directories by cd command.

For example, assume that skirit.metacentrum.cz frontend is down and you want to access brno2 storage:

user123@user123-XPS-13-9370:~$ ssh tarkil.metacentrum.cz # login to "tarkil" instead
...
(BULLSEYE)user123@tarkil:~$ pwd
/storage/praha1/home/user123   # I am on "praha1" storage, but need "brno2"
(BULLSEYE)user123@tarkil:~$ cd /storage/brno2/home/user123 # change to home on "brno2" storage
(BULLSEYE)user123@tarkil:/storage/brno2/home/user123$ pwd 
/storage/brno2/home/user123 # I am now on "brno2" storage