How to gain more space on your N: drive

All users of the Unix system have a quota setup for them limiting how much disk space they can use (for Windows users, this means your N: drive is quoted). The 'typical' user has 100MB of space, this can be changed if need be. If you find you are working with large documents or images and the 100MB isn't enough for you but the work you are doing only requires temporary storage of files, then the best option for you is to use scratch space.

Scratch space refers to various disks which can hold a large amount of data. These disks are not backed up, but the data on them is not removed or deleted, unless there is a hardware fault. Therefore it is safer to keep data on these instead of using your local pcs hard disk. We recommend that the type of data you keep there is data that can be regenerated eg the output from a program or .dvi files.

You can use as much scratch space as you need, remembering that it is a shared resource. The file /usr/damtp/info/scratch contains a list of the computers with scratch space, what group (e.g. GR, HEP, POP) each of the computers belongs to, how much scratch space it has and how much is unused, in the form

To be able to use scratch space, you need to create what's called a symlink in Unix before you can use this extra space in Windows. Use Exceed to log onto a Unix computer. Once logged in, you need to change directory to the name of the scratch space in the above list eg /home/scratch/nipah and then into the public directory, ie;

cd /home/scratch/nipah/public

Now create a directory for yourself (most people use their login name for the directory name) and keep your files in there, ie;

mkdir fe862

You do not need to be logged into a computer to use its scratch space and all damtp unix computers can access each others scratch spaces, so that if you are logged into nipah you can still use narmada's scratch space by running the command

cd /home/scratch/nipah/public

Files held in these directories are not deleted automatically so you should tidy up when your files are no longer needed.

The list above mentions which group a scratch directory is in, please only use scratch directories from the PUB group and any groups that you are a member of. If you are unsure which computers you have access to use the command access-list (in Exceed) to find out which computers you can log into.

Once you've created your directory in the scratch space on a machine, you might want to check and change the security options on that directory so that no one else can read your files. To do this you need to use another Unix command, chmod. To do this, in Exceed, make sure you are not in the directory you've just created (the one named after your login name). You want to be in the folder called public (ie, /home/scratch/nipah/public). Now type in;

chmod 700 your-login-name

You've now created a folder that only you can read and write to. The last part of this procedure is to create a symlink to this new folder. To do this you need to go back to your home directory. To do this, still in Exceed, type;

cd

You should now be able to see the same files that you see when looking at your N: drive by typing in ls -al (ignore all the files starting with a dot '.'). To create the symlink, type;

ln -s /home/scratch/nipah/public/your-login-name nipah_scratch

For example, the user fs862 would type in;

ln -s /home/scratch/nipah/public/fs862 nipah_scratch

The last part of the line, 'nipah_scratch' can be anything. Calling after the name of the scratch location plus the '_scratch' just helps you know what this folder is when you are using Windows Explorer or Word for example.

You have now finished with the Unix commands and you can close Exceed if you don't want it anymore. The last stage is to check to make sure you can read and write to this scratch space from within Windows. Open Windows Explorer and look at the N: drive. Find the folder called nipah_scratch (or whatever you called it when you created the symlink), open it. Initially it will be empty, try copying some files into it, they should appear in this new folder. If everything has been set up correctly, you should be able to put as much work in this new folder as you wish but remember, none of the scratch space gets backed up, you have been warned.