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Faculty of Mathematics

Store, Data and Scratch Spaces

Store spaces are backed up to a secondary machine. Neither data or scratch is backed up.

Data storage areas are nfs exported across the network (e.g. /data/septal/) and typically on reliable hardware (RAID). Data areas are not deleted unless there is a hardware/software/human fault or by request of the owner of the storage.

Scratch storage areas are usually cleared during re-installation and are available locally (as /local/scratch/public/).

Classes of storage

The current classes of storage are:

Storage class Description
Home directories Very Reliable for valuable data. Quota'd, backed up regularly (more than once a day), archived (6 months of) and mirrored. /home/CRSID/
Store Reliable for valuable data. No per user quota. Mirrored regularly, optional limited backups (2 weeks of). No archiving. /store/GROUP/CRSID/
Data Reliable network Scratch Storage for longer term storage of data. No quotas, not backed up, unlikely to be lost/deleted unless there is a hardware failure. /data/septal/CRSID/
We do not expect to commision any more of this type of storage - we offer /store/ instead.
Scratch local access only, no quotas, not backed up, VERY likely to be lost when a machine is upgraded, re-installed or if there is a hardware fault. Mainly intended for short term use by jobs running on the machine where the scratch storage is local. /local/scratch/public/CRSID/

Disks filling up

While there are no quotas on store, data and scratch spaces, when a partition fills up it causes problems for everyone with files on that partition. (/store reports that a particular store space has filled up with a quota exceeded message). Some tips to avoid overfilling the disks:

  • To check the total usage and space available on a partition, cd to a directory on that partition and type df -h
  • To check your own usage, cd to your store/data/scratch space and type du -sk * .??* | sort -n. This will list all your files and subdirectories in increasing order of size.
  • The page on quotas has more tips on reducing your disk usage.

Use of Store

What store space you have access to depends on whether your department or research group has bought in to the store service. You can see what store space you have by typing:

store-space

This will tell you which store spaces you have access to:

You have access to:
        DPMMS

Type store-space create <GROUPNAME> to create your space

If you now type store-space create DPMMS, the system will create for you a directory /store/DPMMS/abc99 (where abc99 is your login name). You can now access this location from Unix from the command line or from the Unix graphical environment.

Store space is also accessible from Maths Windows machines. Just visit \\store.maths.cam.ac.uk\DPMMS\abc99 in a Windows Explorer window. If accessing store from a laptop network Windows machine, you may need to provide your Maths username in the form maths\abc99 and enter your Maths password.

Finally, if you create a public_html directory in your store space, the contents of that directory will be accessible over the web via http://store.maths.cam.ac.uk/DPMMS/abc99/.

Snapshots (backups)

If you want it to, Store can automatically create snapshots of data stored in per-user directories so you can recover old versions of your files. To activate this feature use the store-space snapshots command, e.g.:

store-space snapshots DAMTP

You can turn the snapshots off again (which you may wish to do if the store you are using is full) with store-space nosnapshots.

To access snapshots just look in the .zfs/snapshots/ subdirectory of your user directory (e.g. /store/DPMMS/abc99/.zfs/snapshots/) and you will see directories named zfs-auto-snap with a time and date. Note that the time is in GMT all year round! To retrieve files from these snapshots, simply copy them with cp.

Use of Data and Scratch

We recommend that the type of data you keep here is data that can be regenerated e.g. the output from a program or information that you have copies of on other systems, CDs/DVDs or external (USB) storage etc.

Please do take the time to consider where the best location for your work is. In particular, please ensure all of your original work, including source code, is kept on a drive which is regularly backed up. To be clear, /data and /scratch are not backed up.

Using the command line to access Data spaces

To access the Scratch space on your local machine, change directory to /local/scratch/public and make yourself a directory - most people use their login name for the directory name.

cd /local/scratch/public
mkdir abc99 # Replace abc99 with your login name

Data spaces are accessible over the network, so there are two ways of accessing them. You can log into the machine with the data space, change directory to /local/data/public and create your directory. Or you can just change directory to /data/machine_name e.g /data/unfair before creating your data directory.

ssh unfair
cd /local/data/public
mkdir abc99
cd /data/unfair
mkdir abc99

Sometimes it may look as if a particular computer cannot see another computer's data space. This happens when you (for example) use ls /data/ -- all you see is the data spaces already mounted (if any). But you can still access the Data space if you use the complete name. This is due to the auto-mounter only having those spaces actually in use mounted at any given time.

Using Gnome to access Data spaces

Open the Computer icon on the desktop. From there click on the icon to the left that looks like a pencil on a paper. This will cause the Location text area to appear to the right.

In this Location text-area put the full path to the space you are trying to access. In this example we want to use actin's data space (available only to biophys members) and so we put /data/actin in the location bar and press return.

Create a new folder for yourself, typcially named after your login-name. You place all your files in here.

A tip. Put a soft-link in your home directory like so:

cd
ln -s /data/septal/CRSID ./septal-CRSID
where CRSID = your login ID

And then you can use Gnome to browse to the septal-CRSID subdirectory of your home directory. Or use a Windows computer and look in your home directory (N: drive).

To delete any files you create, highlight the file(s) and press shift-delete. Don't use the usual "move to Trash" as this fails and causes a "Not on the same filesystem" error message window to appear.

Rules Concerning Data and Scratch spaces

You can use as much PUB and SYSTEM Data or Scratch space as you need, remembering that it is a shared resource. The file /alt/ssetup/adm/diskspace contains a list of the Data and Scratch space, what group each of the computers belongs to, how much scratch space it has and how much is unused, in the form:

Data Store             Group           Total G  Free G
/data/squiffy          PUB2011           465.5 UNKNOWN
/scratch/squiffy       PUB2011           136.3 UNKNOWN
/scratch/squint        PUB2011           160.3   159.8

You can also find this information on the list of Maths Linux computers.

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(s) a Data or Scratch space belong to, please only use data stores from the PUB, SYSTEM or any groups that you are a member of. If you are unsure which computers you have access to see the interactive computer list to find out which computers you can log into.