Filer review

This is an evolving early-draft report by the ad-hoc Filer Working Group, who started in early 2012 to review the use and configuration of the departmental filer. For more information about the filer, there are also the departmental filespace user documentation, some notes on the NetApp file server by and for sys-admin, and its own man pages.

The Computer Laboratory has operated a centrally provided NFS file store for Unix/Linux systems continuously since the mid 1980s. This service hosts the commonly used home directories and working directories of most users, and is widely used by research groups to collaborate, via group directories for shared project files and software. At present, this service is provided by a NetApp FAS3140-R5 storage server "elmer" (SN: 210422922), running under "Data ONTAP Release 7.3.3". This server also provides access to the same filespace to other operating systems via the CIFS and WebDAV protocols. It also hosts disk images for virtual machines, which are accessed over block-level protocols such as iSCSI. An additional FAS2040-R5 server "echo" (SN: 200000186549) handles off-site backup using SnapVault.

Review

The Computer Laboratory's IT Advisory Panel initiated on 28 October 2011 an ad-hoc working group to review the provision of departmental file space, headed by Markus Kuhn. The initial focus of this review will be the configuration and use of the existing filer "elmer", with a particular view on identifying and eliminating obstacles that currently prevent remote NFS access by private Linux home computers (something that has long been available to Windows users). It is believed that this project also provides an opportunity to rid the configuration of the filer from historic baggage and to streamline and simplify its use by departmentally administered Linux machines. The working group may later extend its remit and welcomes suggestions.

The initial fact-finding phase of the review was conducted by Markus Kuhn and Martyn Johnson and focussed namespace management, authentication, and access from outside the department.

Namespace management

The NetApp operating system requires filer administrators to structure the storage space at several levels. Familiarity with these will help to understand some of the historic design decisions made.

• An aggregate is a collection of physical discs, made up of one or more RAID-sets. It is the smallest unit that can be physically unplugged and moved intact to a different filer. Elmer has two aggregates because one cannot mix different major disk technologies (Fibre Channel vs. SATA) in an aggregate. The backup filer eldo has just one. Discs can be added to an aggregate on the fly, but never removed.

• A volume is a major unit of space allocation within an aggregate. Typically, they have reserved space, though it is possible to over-commit if one really wants to. Many properties are bound to a volume, e.g. language(?). Significantly, a volume is the unit of snapshotting – each volume has its own snapshot schedule and retention policy.

• A q-tree ("quota tree") is a magic directory within the root directory of a volume which has a quota attached to it and all its descendants. (This is merely for quota; there is no space reservation associated with a q-tree.)

When we first got the filer in 19??, the aggregate layer did not exist, and a volume was just a collection of discs. As a result, ...