Choosing Storage

Before you implement your storage management approach, you need to decide what kinds of storage devices to use. This set of guidelines compares the various types of storage to help you choose. Additional sets of guidelines apply to specific types of storage as implemented in Solaris Volume Manager. See specific chapters about each volume type for details.

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Note –

The types of storage that are listed here are not mutually exclusive. You can use these volumes in combination to meet multiple goals. For example, you could first create a RAID-1 volume for redundancy. Next, you could create soft partitions on that RAID-1 volume to increase the possible number of discrete file systems.

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The following table provides a comparison between the features available for each type of storage.

Table 2–1 Comparison of Types of Storage

Requirements	RAID-0 (Concatenation)	RAID-0 (Stripe)	RAID-1 (Mirror)	RAID-5	Soft Partitions
Redundant data	No	No	Yes	Yes	No
Improved read performance	No	Yes	Depends on underlying device	Yes	No
Improved write performance	No	Yes	No	No	No
More than 8 slices per device	No	No	No	No	Yes
Larger available storage space	Yes	Yes	No	Yes	No

The following table outlines the trade-offs in write operations, random reads, and hardware costs between RAID-1 and RAID–5 volumes.

Table 2–2 Optimizing Redundant Storage

	RAID-1 (Mirror)	RAID-5
Write operations	Faster	Slower
Random read	Faster	Slower
Hardware cost	Higher	Lower

The following list summarizes the information outlined in the tables:

• RAID-0 volumes (stripes and concatenations) and soft partitions do not provide any redundancy of data.

• Concatenation works well for small random I/O operations.

• Striping performs well for large sequential I/O operations and for random I/O operations.

• Mirroring might improve read performance, but write performance is always degraded in mirrors.

• Because of the read-modify-write nature of RAID-5 volumes, volumes with over 20 percent writes should not be RAID-5. If redundancy is required, consider mirroring.

• RAID-5 writes cannot be as fast as mirrored writes, which in turn cannot be as fast as unprotected writes.

• Soft partitions are useful for managing very large storage devices.

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Note –

In addition to these generic storage options, see Hot Spare Pools for more information about using Solaris Volume Manager to support redundant devices.

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