11.2 Planning OES File Storage

Storage Services (NSS)

The Storage Services file system is used in NetWare 5.0 and above, is included in the Open Enterprise Server.

The NSS file system is unique in many ways, especially in its ability to manage and support shared file services from simultaneous different file access protocols. It is designed to manage access control (using a unique model, called the OES Trustee Model, that scales to hundreds of thousands of different users accessing the same storage securely) in enterprise file sharing environments.

NSS and its predecessor NWFS are the only file systems that can restrict the visibility of the directory tree based on the user ID accessing the file system. NSS and NWFS have built-in ACL (access control list) rights inheritance. NSS includes mature and robust features tailored for the file-sharing environment of the largest enterprises. The file system also scales to millions of files in a single directory. NSS also supports multiple data streams and rich metadata; its features are a superset of existing file systems on the market for data stream, metadata, name space, and attribute support.

Both eDirectory and Active Directory are supported as identity sources, and OES enables the NSS file system to accept Active Directory identities as trustees. Active Directory users can authenticate to Active Directory and natively access the NSS resources using the CIFS protocol.

Btrfs

BtrFS creates a default subvolume in its assigned pool of space. It allows you to create additional subvolumes that act as individual file systems within the same pool of space. The number of subvolumes is limited only by the space allocated to the pool.

If BtrFS is used for the root (/) file system, you can cover any subdirectory as a subvolume as you might normally do. You should also consider covering the following subdirectories in separate subvolumes because they contain files that you might prefer not to snapshot for the reasons given:

Ext2

Ext2 does not maintain a journal, so it is generally not desirable to use it for any server that needs high availability, with one important exception. If a paravirtualized server is running as a Xen VM guest, you should format the /boot partition with Ext2 as explained in Section 7.4, Xen VMs Need Ext2 for the System /Boot Volume.

Ext3

The Ext3 file system is a journaled file system that has the widest use in Linux today. It is the default file system for SUSE Linux 12 distributions. It is quite robust and quick, although it does not scale well to large volumes or a great number of files.

A scalability feature has been added called H-trees, which significantly improved Ext3's scalability. However, it is still not as scalable as some of the other file systems. With H-trees, it scales similarly to NTFS. Without H-trees, Ext3 does not handle more than about 5,000 files in a directory.

Reiser

Reiser was designed to remove the scalability and performance limitations that exist in Ext2 and Ext3 file systems.

Reiser scales and performs extremely well on Linux, outscaling Ext3 with H-trees. In addition, Reiser was designed to use disk space very efficiently.

XFS

The XFS file system is open source and is included in major Linux distributions. It originated from SGI (Irix) and was designed specifically for large files and large volume scalability.

Video and multimedia files are best handled by this file system. Scaling to petabyte volumes, it also handles very large amounts of data. It is one of the few file systems on Linux that supports HSM data migration.

Collaboration (GroupWise)

GroupWise deals with many little files. Because only the application process is accessing the file system, the added overhead of the rich ACL and file attributes found in NSS is redundant. The necessary characteristics are a file system whose performance remains relatively constant regardless of the number of files that are in the volume, and that performs well with small files. GroupWise recommends the Ext3 file system. NSS and Reiser are also supported.

Dynamic Storage Technology

Dynamic Storage Technology does not depend on a particular file system in principle; however, it is currently supported only on NSS volumes.

File Serving

Generally there are two types of NAS use cases: Serving files to application servers in a tiered service oriented architecture (SOA), and serving files to end user desktops and workstations. The former has minimal access control requirements. The latter has quite heavy access control requirements.

Typically for serving files to application servers (traditional NAS), you would choose a file system that is scalable and fast. Reiser and XFS would be good choices in this environment. For file serving to end user workstations, the access control and security management capabilities of the NSS file systems with AFP, CIFS, and NCP file access protocols are important.

The NSS model does better than the other file systems for very large numbers of users. It allows for security between users and also allows for very fine granular sharing between given users and groups. NSS includes a visibility feature implemented in the file system that prevents unauthorized users from even seeing subdirectory structures they don't have rights to access.

Cluster Services

Cluster Services does not depend on a particular file system. For shared storage, the file systems software must be available from node to node. For example, if you are using NSS on one node, you need to use NSS on the failover node as well.

Printing (iPrint)

iPrint is file system agnostic. There is no noticeable difference in performance or reliability on any of the file systems.