Novell Storage Services

Novell Storage Services (NSS) is a powerful storage and file system that provides an efficient way to use all the space on your storage devices. The first concept with which you should become familiar in the NetWare file system is the volume . A NetWare volume is the highest level in the file system hierarchy, and is the structure within which directories and files are maintained . Each NetWare server will have at least one volume, SYS , which contains all the NetWare system files and utilities. You can then create additional volumes on the server as necessary to serve your file-management needs.

The volume is the last link in the NSS chain. Figure 8.1 gives a high-level view of the NSS architecture.

• NSS partitions: A partition is a logical organization of space on a hard disk, and represents the lowest level of organization for disk storage. Partitions prepare space on storage devices to be used in an organized and structured way by defining the ways in which the file system will interact with the storage devices.

• NSS storage pools: NSS storage pools are created in partitioned space. A storage pool is a specified amount of space you obtain from all your storage devices. Within the storage pool, you will create the NSS volumes you need on the server. Only one storage pool can exist on a partition, but you can create an unlimited number of NSS volumes in each storage pool, thereby removing partition constraints to the number of volumes that can be created.

• NSS volumes: The volumes you create from NSS storage pools are called logical volumes . As noted in Figure 8.1, they are logical volumes because the space used to create a given volume can come from a variety of storage devices. It is not contiguous space. A logical volume can be set to a specific size, or allowed to grow dynamically according to the amount of physical space assigned to the pool. This lets you add and store any size or any number of files you need without having to create other partitions. You can add any number of volumes to a storage pool as long as you have available physical space in the pool.

Figure 8.1. A high-level view of the NSS architecture.

Beyond these three NSS building blocks, you should be aware of several concepts related to the configuration and management of NSS volumes:

• NSS management: You will use NoRM for configuring and managing your NSS environment. It gives you the ability to control and change your server's storage characteristics from any place with an Internet connection.

• Overbook your storage pool: Individual logical volumes cannot exceed the size of a storage pool. However, because you can create multiple logical volumes in a single storage pool, NetWare 6.5 permits the total space allocated to logical volumes to exceed the actual pool size. This feature, called overbooking , can be an efficient way to manage your file system because it lets your volumes grow organically over time instead of being locked into a rigid structure that can leave space unused.

• Deactivate/activate logical volumes and storage pools: You might need to temporarily prevent user access to storage pools or volumes to perform maintenance. Instead of bringing down the server, you can deactivate individual storage pools. When you deactivate a storage pool, users will not have access to any of the volumes in that pool.

• Fast error correction and data recovery: Because NSS is a journaled file system, it can quickly recover data after a file system crash. Instead of scanning the file system for corruption, NSS replays the latest set of changes to make sure they were written correctly. The file system either recovers the changed information or returns it to its original condition prior to the transaction.

• Immediately save data to disk: The Flush Files Immediately feature saves your file data to disk immediately after you close the file instead of caching it in memory and waiting for the next disk write cycle. This prevents your data from being at risk between disk write cycles, at the cost of slower file system performance overall.

• Retain previously saved files (Snapshot): The File Snapshot feature keeps an original copy of all open files so they can be archived by your backup utility. By capturing the most recent closed copy of the file, Snapshot guarantees that you still have a solid copy of the file with which to work. NetWare 6.5 also offers pool snapshots, so you can preserve a view of an entire storage pool at any point in time. This option can be a valuable addition to your data protection and archive capabilities.

• Transaction Tracking System (TTS): Transaction Tracking System protects database applications by backing out transactions that are incomplete due to a system failure. To enable TTS for an NSS volume, type the following command at the server console. You can also place the NSS transaction command in your AUTOEXEC.NCF so that TTS starts automatically.

   nss /transaction=<  volume name  > 

• Review the modified file list: NSS maintains a list of files that have been modified since the previous backup. To save time, your backup utility has to review only this list rather than scanning the entire file system for modified files.

• Enable file compression: NSS supports file compression. This lets you decide whether to compress the files in your volumes for more efficient use of storage device space. Once it's enabled, however, you cannot disable file compression without re-creating the volumes.

• Data shredding : The data shredding feature overwrites purged disk blocks with random patterns of hexadecimal characters . This is a security option that helps prevent the use of a disk editor to attempt to recover purged files. You can require up to seven random shred patterns be written over deleted data.

• User space restrictions: From iManager, you can now limit the amount of space available to an individual user on a logical volume.

• Directory space restrictions: From iManager, you can now limit the space that can be assigned to a given directory or subdirectory.

• CD-ROMs as read-only logical volumes: NSS offers full CD-ROM support for ISO9660 and HFS formats. Simply insert the CD-ROM into the server-mounted CD-ROM drive and it will be automatically mounted as a new NSS volume.

• No memory required for mounting volumes: NSS does not require large amounts of memory to mount volumes because it does not scan the entire file system during the mounting process. After the mounting is complete, NSS does not load files into memory until you access them. Therefore, no additional memory is required when you add files and mount volumes.

• Hot fix: Over time, sections of your server hard disks might start to break down and lose their ability to reliably store data. NSS supports hot fix to prevent data from being written to unreliable blocks. Hot fix redirects the original block of data to the hot fix redirection area, where the data can be stored correctly. To redirect a block of data, the operating system records the address of the defective block. Then the server no longer attempts to store data in that block. By default, two percent of a disk's space is set aside as the hot fix redirection area. You can increase or decrease this amount. If hot fix is enabled, it is always active unless the disk fails or the redirection area is full. You can view hot fix activity in NoRM by selecting the Disk/LAN Adapters link. Click on the disk adapter to which the drive is attached and click the appropriate drive link. The Redirection Blocks column will show you how many blocks have been redirected to the hot fix area.

  WARNING

  If you notice the number of redirected blocks increasing, it's a sign that your drive is ready to fail. You should immediately back up your data and replace the drive to prevent an unplanned outage .

  
  

  TIP

  You can disable the hot fix redirection area when you create disk partitions, which will save partition space. This can be useful if you are using a RAID system that provides its own fault tolerance. If you do not enable hot fix when the partition is created, you can add it later only by deleting the volumes from the partition, adding hot fix, and restoring the volumes from a backup.

  
  

• Repair storage pools instead of individual volumes: Use the repair utilities VERIFY and REBUILD to repair NSS systems. VERIFY and REBUILD function on the pool level rather than the individual volume level. Unlike VREPAIR for traditional NetWare volumes, these utilities should be used only as a last resort to recover the file system after data corruption.

  • VERIFY checks the file system integrity for an NSS pool by searching for inconsistent data blocks or other errors. This utility indicates whether there are problems with the file system.

  • REBUILD verifies and uses the existing leaves of an object tree to rebuild all the other trees in the system. You need to deactivate pools (and all the volumes in the pools) before you run REBUILD so that users cannot access the volumes you are rebuilding. When you deactivate a storage pool, all the volumes in the pool automatically deactivate.

• RAID support: NSS provides software support for RAID 0 (data striping), RAID 1 (data mirroring), and RAID 5 (data striping with parity) to give you a robust set of options for protecting your server data. You can create and manage software RAID through iManager or through the console-based NSS Management utility (NSSMU).

Understanding these NSS concepts will make it easier for you to plan and manage your NetWare file system.