Planning Your Storage Configuration
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This chapter introduces you to the Sun StorageTek Common Array Manager storage components. It contains the following sections:
For more information about the concepts introduced in this chapter, see the appropriate topic in the online help.
Storage Array Configuration Components
The array management software configures both physical and logical storage components. The components of a storage array configuration are as follows.
- Initiator - A port on a Fibre Channel (FC) host bus adapter (HBA) that allows a host to gain access to the storage array. The initiator has a World Wide Name (WWN) that is globally unique.
- Host - A data host, or server with one or more initiators, that stores its data on arrays. You can define volume-to-logical unit number (LUN) mappings to an individual host or assign a host to a host group.
- Host group - A collection of hosts that share access to the same volumes.
- Storage domain -A logical entity used to partition storage. You need to purchase a license for the number of domains you need, depending on your array.
- Storage profile - A defined set of characteristics for a storage pool. You can choose from the set of preconfigured profiles or create a new one.
- Storage pool - A collection of volumes that share a profile defining a common configuration.
- Volumes - A division of a storage pool, consisting of virtual disks, representing the storage space that is used by the data hosts in the environment.
- Disk - A non-volatile, randomly addressable, rewriteable data storage device. Physical disks are managed as a pool of storage space for creating volumes.
- Virtual disks - Also called a redundant array of independent disks (RAID) set, a collection of locations in the memory of more than one physical disk. The storage array handles a virtual disk as if it were an actual disk.
- Tray - An enclosure that contains a varying number of disks, depending on your array.
In addition to the basic elements of your storage configuration covered in this guide, you can add advanced, premium features to your configuration. These features require the purchase of licenses. The following premium features are described in the online help and user guide:
- Snapshots are copies of the data in a volume. They offer a high-availability alternative to backups because you do not need to take the array offline to create the snapshot, and you can store the snapshots in less space than the original data.
- Volume copies are copies of the complete contents of one data volume that are located on another data volume on the same array.
- Replication sets are the association between primary and secondary volumes. The secondary volume contains a complete copy of the data on the primary volume. The data replication software continuously replicates the data between volumes in a replication set.
Partitioning Storage Using Storage Domains
Storage domains, also called sets or storage partitions, enable you to partition storage to allow hosts or host groups access to specific volumes. Data hosts, such as a data base server, initiate data to store in volumes through the physical host ports (or initiators), residing on host HBAs. Volume-to-LUN mapping enables you to specify the host or host group that can access a specific volume on your storage array.
Note - Storage domains for LUN-mapping require the purchase and activation of a license. (Exception - the Sun StorageTek 6130 array includes some free storage domains to start.) The role of the free default domain is discussed below.
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There is a free default domain with limited functions noted below. But to map specific initiators to specific volumes, you need to activate a premium license for a storage domain. Usually your need for premium licenses will be determined at the time you order your array.
The Default Domain
A non-premium, default storage domain exists to include the following:
- All host groups and hosts that are not explicitly mapped to a volume.
- All volumes that have a default volume-to-LUN mapping assigned.
- All unmapped, automatically detected initiators.
Any volumes within the default storage domain can be accessed by all hosts and host groups within that storage domain.
Note the following concerning default domains:
- LUN-mapping cannot be configured.
- Initiators are created but remain in the default domain until mapped.
- Hosts and host groups can be created but have no valid purpose without a storage domain.
Premium Storage Domains
Premium storage domains define a volume-to-logical unit number (LUN) mapping, which will allow you to specify the host or host group that will have access to a particular volume in your storage array. The storage domain designates that only the selected host or host group has access to that particular volume through the assigned LUN.
When the storage domain consists of a volume mapped to a host group, it can enable hosts with different operating systems (heterogeneous hosts), to share access to a storage volume. A host within a host group can be mapped separately to a different volume.
A storage domain can contain up to 256 volumes. A volume can be included in only one storage domain and each LUN, from 0 to 255, can only be used once per storage domain.
Note: Not all operating systems support up to 256 LUN IDs. See the documentation for your operating system for more information.
FIGURE 4-1 shows how storage domains can be used to partition storage. It depicts a storage array configured with three storage domains, Storage Domain 1, Storage Domain 2, and Storage Domain 3.
FIGURE 4-1 Storage Array With Three Domains and Four Data Hosts
Storage Domain 1 consists of two volumes, Marketing and Sales, that are mapped to Host Group X. Host Group X contains two hosts, Host A and Host B. All initiators associated with Host A and Host B, within Host Group X, have access to volume Marketing by way of LUN ID 1 and to volume Sales by way of LUN ID 2.
Storage Domain 2 consists of one volume, Engineering, that is mapped to Host Group Y. Host Group Y contains two hosts, Host C and Host D. By virtue of being associated with any host within Host Group Y, all initiators associated with Host C and Host D have access to volume Engineering by way of LUN ID 1.
Storage Domain 3 consists of one volume, Test, that is mapped to Host D. All initiators associated with Host D have access to volume Test by way of LUN ID 2. Note that Host D is a member of Host Group Y; however, since volume Test is mapped directly to Host D and not to Host Group Y, Host D is the only member of Host Group Y that can access volume Test.
Note - LUN IDs must be unique within a storage domain.
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For more information about storage domains and LUN mapping, see the online help.
Best Practices - Storage Configuration
When configuring a storage array, you need to determine how to organize and allocate the total storage capacity into volumes and share those volumes among your data hosts. As you plan your storage configuration, it is important that you consider the following requirements for your site:
- Performance requirements - You can optimize I/O activity by selecting a predefined storage profile with different characteristics or by creating a custom profile.
- Access requirements - You can use storage domains to organize and allocate storage so that only certain hosts have access to volumes. Volumes in a storage domain can be accessed only by hosts and host groups that are in the same storage domain. You can associate a storage domain with individual hosts or with a host group.
- Combination of redundancy with performance - To maximize both performance and redundancy, a combination of RAID levels is necessary. The data striping provided by RAID 0 is a cost-effective way to create high levels of performance in a disk array, and having multiple copies of data through data mirroring provided by RAID 1 is the best way to create redundancy. By combining RAID 1 with RAID 0, you can take advantage of both features.
To combine disk mirroring with disk striping, configure RAID 1 with more than five drives. The firmware automatically creates a RAID 1+0 virtual disk.
- Storage defaults - The default storage profile, storage pool, and storage domain are configured as follows:
- The default storage profile configures associated volumes with a RAID-5 level, default segment size, enabled read-ahead mode, FC disk type, and a variable number of drives.
- The default storage pool uses the default profile (RAID-5) and groups all volumes with the same storage characteristics, as defined by the storage profile.
- The default domain has no restrictions and allows all hosts and host groups to share access to the same volumes. If you want to restrict access to volumes from certain hosts, you should use storage domains and not the default domain.
- Using profiles and pools - You must plan your configuration to determine what storage profile and storage pool to use. For more information, see Planning Volumes and related topics in the online help.
Sun StorageTek Common Array Manager Software Installation Guide
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820-7921-10
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