Introduction to Storage Management

Storage management is the means by which you control the devices on which the active data on your system is kept. To be useful, active data must be available and remain unchanged (persistent) even after unexpected events (hardware failure, software failure, or other similar event).

Storage Hardware

There are many different devices on which data can be stored. The selection of devices to best meet your storage needs depends primarily on three factors:

• Performance

• Availability

• Cost

You can use Solaris Volume Manager to help manage the tradeoffs in performance, availability and cost. You can often mitigate many of the tradeoffs completely with Solaris Volume Manager.

Solaris Volume Manager works well with any supported storage on any system that runs the Solaris^TM Operating Environment.

RAID Levels

RAID is an acronym for Redundant Array of Inexpensive (or Independent) Disks. Basically, this term refers to a set of disks (called an array, or, more commonly, a volume) that appears to the user as a single large disk drive. This array provides, depending on the configuration, improved reliability, response time, and/or storage capacity.

Technically, there are six RAID levels, 0-5,. Each level refers to a method of distributing data while ensuring data redundancy. (RAID level 0 does not provide data redundancy, but is usually included as a RAID classification because it is the basis for the majority of RAID configurations in use.) Very few storage environments support RAID levels 2, 3, and 4, so they are not described here.

Solaris Volume Manager supports the following RAID levels:

• RAID Level 0–Although they do not provide redundancy, stripes and concatenations are often referred to as RAID 0. Basically, data are spread across relatively small, equally-sized fragments that are allocated alternately and evenly across multiple physical disks. Any single drive failure can cause data loss. RAID 0 offers a high data transfer rate and high I/O throughput, but suffers lower reliability and availability than a single disk

• RAID Level 1–Mirroring uses equal amounts of disk capacity to store data and a copy (mirror) of it. Data is duplicated, or mirrored, over two or more physical disks. Data can be read from both drives simultaneously (either drive can service any request), providing improved performance. If one physical disk fails, you can continue to use the mirror with no loss in performance or loss of data.

  Solaris Volume Manager supports both RAID 0+1 and (transparently) RAID 1+0 mirroring, depending on the underlying devices. See Providing RAID 1+0 and RAID 0+1 for details.

• RAID Level 5–RAID 5 uses striping to spread the data over the disks in an array. RAID 5 also records parity information to provide some data redundancy. A RAID level 5 volume can withstand the failure of an underlying device without failing, and, if used in conjunction with hot spares, can withstand multiple failures, albeit with a substantial performance degradation when operating with a failed device.

  In the RAID 5 model, every device has one area that contains a parity stripe and others that contain data. The parity is spread over all of the disks in the array, reducing the write time for large independent writes because the writes do not have to wait until a single parity disk can accept the data.