Introduction to Storage Management
How you choose to manage your storage determines how you control the devices
that store the active data on your system. To be useful, active
data must be available and remain persistent even after unexpected events, such as a
hardware or software failure.
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 trade-offs in
performance, availability, and cost. You can often mitigate many of the trade-offs with
Solaris Volume Manager.
Solaris Volume Manager works well with any supported storage on any system that
runs the Solaris operating system.
RAID Levels
RAID is an acronym for Redundant Array of Inexpensive (or Independent) Disks. RAID
refers to a set of disks, called an array or a volume, that
appears to the user as a single large disk drive. Depending on
the configuration, this array provides improved reliability, response time, 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 anyway. RAID Level
0 provides the basis for the majority of RAID configurations in use.)
Very few storage environments support RAID Levels 2, 3, and 4, so those
environments are not described here.
Solaris Volume Manager supports the following RAID levels:
RAID LEVEL 0 – Although stripes and concatenations do not provide redundancy, these volumes 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 lower availability than a single disk.
RAID Level 1 – Mirroring uses equal amounts of disk capacity to store data and a copy (mirror) of the data. Data is duplicated, or mirrored, over two or more physical disks. Data can be read from both drives simultaneously, meaning that either drive can service any request, which provides 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 volumes. 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-5 volume can withstand the failure of an underlying device without failing. If a RAID-5 volume is used in conjunction with hot spares, the volume can withstand multiple failures without failing. A RAID-5 volume will have 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 other areas that contain data. The parity is spread over all of the disks in the array, which reduces the write time. Write time is reduced because writes do not have to wait until a dedicated parity disk can accept the data.
