Calculus data storage server

Some time after Maths departmental home directories migrated from the former geometry2 fileserver to ICT storage in 2007, we started to run out of space on the new ICNFS storage service and it wasn't very long before geometry2 was brought back out of retirement, renamed as calculus and rebuilt with an additional 14-disk array attached to provide 1.7 Tb of local storage. This server was shared via NFS to all of the Maths and Stats compute cluster nodes.

Over Christamas 2015, we ran into a technical issue with the ZFS filesystem on this server caused by a user who was storing a large number of very small files on calculus; this 32-bit server's limited memory could not cope with the large numbers involved and started to crash randomly. In January 2016, calculus was replaced by a new 64-bit server with 16 TB of installed disk, providing over 10 TB of user storage.

Where is the calculus filespace?

To retain backwards compatibility with the original 32-bit calculus server, which had some technical constraints on disk layout, there are 3 separate storage pools on calculus called home, bitbucket1 and bitbucket2 respectively and these are mounted on Maths systems as follows:

• home: /home/calculus/home

• bitbucket1: /home/calculus/bitbucket1

• bitbucket2: /home/calculus/bitbucket2

As with all other Maths storage servers, no disk quotas are imposed but storage usage is monitored and users will be advised if free filespace falls to a low level.

How do I use calculus?

calculus is intended to be accessed only from the systems its filespace is mounted on and you can't log into it directly. To create your own storage folder on calculus, you simply log into any of the Maths systems that mount the calculus filesystems (one of the Maths compute cluster nodes or the Stats cluster) change to one of the three directories listed above and create your own folder. Here's how you do it:

1. log into any compute cluster node or a Stats cluster machine

2. decide where you want to create your folder - in the home area or on one of the two bitbuckets and create your folder using the mkdir command; for example, you might want to create some storage space called 'my_zone' in bitbucket1 so you would type:

   mkdir /home/calculus/bitbucket1/my_zone
   

3. you can name your new folder anything you like although using your username is suggested as it makes it easier for others to see who owns it. Now, if you want to you can restrict access to your new folder to just yourself - this is optional but advisable if you have sensitive data, programs that you have written yourself, etc that you don't want to share with others. You can do this with chmod - here's an example where we change the permissions of the 'my_zone' folder just created to restrict access to the owner only:

   chmod 700 /home/calculus/bitbucket1/my_zone
   

That's all there is to it.

Are disk quotas imposed on calculus?

No! Per-user disk quotas are not imposed as this would defeat the object of this facility. However, there is a finite limit set by the available space in the disk pool - the maximum contiguous file space that can be provided is 10.4 TB.

Is data on calculus backed up?

Yes, it is mirrored daily to ma-backup1 which in turn is mirrored to the Maths offsite server in Milton Keynes.

Can I mount calculus on my own computer via NFS?

At the moment, no because no-one has asked for this facility and for security reasons only known computers are allowed to do this. But this can be arranged on request.

About the calculus server

calculus is a HP N45L MicroServer fitted with 4 x 4 TB disks arranged as a ZFS RAIDz1 pool providing 10.4 TB of usable storage, with /home, /bitbucket1 and /bitbucket2 being ZFS filesystems created in this pool. Calculus runs FreeBSD 10.1 which is installed on an internal 4GB USB pendrive.

Details of the old original calculus server can be found here