Usage Scenarios


Kerberos Tickets:

The PETAL archive uses Kerberos tickets to authenticate against the archive, therefore to access the archive you must have a valid Kerberos ticket. If you try to access the archive and get a permission denied type of error, you probably don’t have a Kerberos ticket setup.

Only some machines in SEE have this functionality on them. Any machine currently running Centos 6 should have this ability. Other authentication methods present such as SSH keys may also have an effect on using Kerberos tickets. You will need to identify a machine that you can use. Try your own machine first and if that doesn’t work, try using foe-linux-01.

You will need to test whether you have a valid Kerberos ticket present on your machine. Run klist and look at the output of the command. If no valid ticket is present, you will need to run the command kinit to create a ticket.

Restrictions On Deleting Files:

Files should be in their final format before they are moved into the PETAL archive. The system is similar to a Write-Once-Read-Many (WORM) device. There is a ‘grace period‘ in place that allows files to be deleted and modified for an hour after the copy. When the ‘grace period’ expires files will be marked as ‘read-only‘ and no further modification will be possible. It is worthwhile checking that only the required files will be archived (before they are) to avoid waste of the purchased storage space. It is advisable to create your directory structure and check that all the files included are the ones you want to preserve on tape before starting the copy. Only under exceptional circumstances will arrangements be made for deleting unnecessary files. You will need to contact the SA to arrange the removal of the files.

Pre-Staging Files:

Due to the way the an Active Archive works, there is no way to know in advance how long it will take to access one of your files, as there are may factors which can influence this.

  1. When was the file last accessed.
  2. Is there a copy of the file within the disk cache.
  3. Is the tape currently loaded in a tape drive and what is the tape drive doing.
  4. How far along the tape is the file located.
  5. Is the tape currently within the tape library or in an offline location.

Displaying a directory listing using “ls” only displays the names of the files, not where the copies are stored. You physically need to open/read or try to copy a file before its contents will be available for you to access. The delay in providing the contents of the file to you will be determined by the previous conditions.

If you know that you want to use a particular group of files in a few hours time, you can pre-stage the files back into the disk cache by accessing them. Below is a list of a few commands that you could use for text files that would achieve this as they will actually try and read the contents of the file.

  • vi filename
  • cat filename
  • head filename
  • tail filename

or in case on the entire directory you could use the following command under the directory of your storage allocation:

  • cat *.* >> /dev/null

to refresh all the files and force them back into the cache. Once the file has been retrieved and a copy placed into the disk cache again, successive accesses to the file will be faster as it will return the file immediately from the disk cache.

Remember that you have no control over how long a copy of the file will remain in the disk cache. If the space within the disk cache is required by another file, files that already have a copy stored on tape will be the first ones to have their copy within the disk cache removed.

Accessing the PETAL Archive Using Unix/Linux:

Follow the instructions for using Kerberos Tickets to see if your nominated machine is compatible with Kerberos.

Once a Kerberos ticket has been created, try to access the archive like you would any Unix/Linux other directory.

cd  /nfs/petal/my_project_folder

You can now create directories and copy files, as you would normally  on a normal file-system.

Remember that is not possible to delete any files once that they have been copied to the tape. Make sure your files are in the final form before starting to copy them. An hour-long ‘grace period’ is in place to allow to delete files copied by mistake. After that period expires they will become read-only.

Accessing the PETAL Archive Using Windows:

To access the PETAL archive under Windows,  you can enter the location of the your project folder in the Address bar of Windows Explorer as shown in the following example:

\\petal-fs.leeds.ac.uk\my_project_folder

You should be able to see and navigate into your storage allocation directory.

Map a network drive using the Tools menu > Map network drive and enter the complete URL with your storage allocation directory included.

You can now create directories and copy files, as you would normally  on a normal file-system. Remember that is not possible to delete any files once that they have been copied to the tape. Make sure your files are in the final form before starting to copy them. An hour-long ‘grace period’ is in place to allow to delete files copied by mistake. After that period expires they will become read-only.

Accessing the PETAL Archive Using Mac OS X:

To access the PETAL archive, you can execute commands from the terminal against the archive using the address below:

smb://petal-fs.leeds.ac.uk/my_project_folder

You should be able to see and to navigate into the your storage allocation directory.

Use the Connect To Server feature of the Finder. Select Go > Connect To, and enter the complete URL with your storage allocation directory included as shown in the example below:

smb://petal-fs.leeds.ac.uk/my_project_folder

You can now create directories and copy files as you would normally on a normal file-system. Remember that is not possible to delete any files once that they have been copied to the tape. Make sure your files are in the final form before starting to copy them. An hour-long ‘grace period’ is in place to allow to delete files copied by mistake. After that period expires they will become read-only.

Copying Files From ARC Machines To The PETAL Archive:

You can use any remote file transfer program that you like to transfer the files. The only other condition that you must obey is that the target SEE machine supports Kerberos tickets. Use the instructions above to verify that your SEE machine supports Kerberos tickets. It is recommended to use one of the existing machines that supports Kerberos, such as foe-linux-01, foe-linux-02 or foe-linux-03.

scp  *  user_name@foe-linux-03:/nfs/petal/my-project/

Instead of pushing the files from ARC to SEE, you can use the reverse of this command and pull the files instead, as long as you do it from a SEE machine that supports Kerberos.

Copying Files From SEE Machines To The PETAL Archive:

Copying files between a SEE machine and PETAL is as easy as copying files between different directories. The only other requisite is that your machine supports Kerberos so that the PETAL file-system under ‘/nfs/petal/my-project/‘ is visible.

Copying Files From The PETAL Archive To SEE Machines:

Copying the files from PETAL to any SEE machine has no restrictions, it is a simple copy from one directory to another. If the machine that you are currently logged into can see the PETAL file-system under the directory ‘/nfs/petal/my-project/‘, then it obviously supports Kerberos tickets.

Copying Files From The PETAL Archive To ARC Machines:

You can use any remote file transfer program that you want as long as you are logged into a SEE machine that can see the file-system under /nfs/petal.

cp -rv  /nfs/petal/my-project/*  user_name@arc1:~/temp

Things to Remember:

The only issues that you may have is that there could be a delay when reading the files from PETAL if the files aren’t in the disk cache. Most commands will wait/suspend whilst the read request is completed. You should also be able to read your data directly from any POSIX complaint software. If the file hasn’t been accessed for a very long time, then the tape may have been removed from the library and stored in an offline location. In this scenario, it could be many hours before the SA sees the request to load the tape, so that the read request can be completed.

It is advisable to create your directory structure and check that all the files present are the ones that need to be preserved on tape before starting the copy. Once the files are copied to your storage allocation they will become read-only in an hour. During this period the system will still allow to delete and modify the files but after the period expires all the files will be marked as ‘read-only‘ and therefore no further modification will be possible.

Make sure you don’t copy files that don’t need to be preserved as it will be impossible to delete them after they have been copied to tape. Only under exceptional circumstances will arrangements be made for deleting unnecessary files from tapes. You will need to contact the SA to arrange the removal of the files.

If you plan on copying a large number of files off PETAL, it would be worthwhile pre-staging the files so that they will be present in the disk cache. This will ensure an instantaneous copy of the file instead of a possible delay whilst loading the tape or if the tapes are stored in an offline location.

For any questions don’t hesitate to contact the SA with the Send a Message form.