Advanced Novell Network Management: NetWare 6

Chapter 6: Configure and Troubleshoot a RAID Solution Using NSS

 

Objectives:

This chapter discusses using a RAID with your NetWare 6 network. The objectives important to this chapter are:

  1. Implement RAID 0 with NSS
  2. Configure Partition Mirroring and Duplexing in NSS
  3. Troubleshoot Software RAID and Mirroring in NSS
Concepts:

RAID stands for Redundant Array of Independent (or Inexpensive) Disks (or Devices). An array of smaller drives can produce better performance than a single larger drive. Some RAID implementations can produce better fault tolerance, some can produce faster read and write service.

Different implementations of RAID are referred to as levels, and as hardware or software RAID.

A hardware implementation would use a RAID controller card for several hard drives. The operating system would communicate with the card. It is up to the configuration of the controller card whether the system sees the drives as one or many.

A software implementation would use software as an interface between the disks drivers and the operating system. This software logically controls several drives as a RAID.

The chapter compares features of hardware and software RAID solutions:

  • software is cheaper
  • hardware is faster
  • management is more complex for software
  • hardware offers more level options
  • hardware works by each hard drive, software works by each drive partition

NSS will support software RAID, levels 0 and 1. It will support hardware RAID, at whatever level you have. Follow the link below to a nice summary of RAID level features not listed in these notes..

RAID levels and features:

  1. Disk striping - writes to multiple disks, does not provide fault tolerance. Performance is increased, because each block of data in a stream is written to the next device in the array. Failure of one device will affect all data.
  2. Mirroring and Duplexing - provides fault tolerance by writing the same data to two drives. Two mirrored drives use the same controller card. Two duplexed drives each have their own controller card.

The text provides instructions for setting up a software implemented RAID 0 with NSS. As noted above, this will provide a performance enhancement by striping data across multiple disks. This will not improve fault tolerance, it will decrease fault tolerance.

To create a RAID 0 array:

  1. Run ConsoleOne and log in as an administrator
  2. Find your server, right click it, and choose Properties
  3. Click the media tab, click RAID devices, and choose New
  4. You will be prompted for RAID Segment Size. Enter the number of Megabytes you want to use from each device available.
  5. In the list of available storage devices, click the check box beside each one to be used in the array, then click the Next button.
  6. On the next screen, enter the Stripe Size as a number of Kilobytes. This size is the amount of data to write to each disk before moving on to the next disk. On the same screen, choose the RAID type, which is 0 in this example.

Each time more devices are added to the RAID, remember to restripe the array. This means to redistribute the data across the devices to make reads and writes faster.

Configure Partition Mirroring and Duplexing

Fault tolerance can be enhanced by mirroring or duplexing a partition. When you set up two hard drives on the same controller to receive the same data, you are mirroring the drives. If one drive should fail, you continue using the other.

Duplexing two drives is the same as mirroring, but duplexed drives each have their own controller. In the rest of the discussion in this chapter, when the text talks about mirroring, this is meant to include duplexing.

With NetWare 6, you can mirror or duplex partitions, not just drives.

  • You can mirror NSS and Traditional partitions, but the mirror must be the same type as the partition it is mirroring.
  • You cannot mirror a pool, except by mirroring each partition in it.
  • Partition mirrors must be within 2 MB of the size of the partitions they mirror.
  • Partitions that will be mirrored must have a hot fix area, the partitions that will mirror them must have a hot fix area as well.
Troubleshoot Software RAID and Mirroring in NSS

Two observations are made about troubleshooting, repeating the information above:

  • A partition and its mirror must be within 2 MB of the same size.
  • Partitions must be created with a hot fix area, or they cannot be mirrored.