Disk arrays trickle down to SMBs
SMB disk array expansion and managementSMB disk arrays start at 1 TB or 2 TB, scaling up to 6 TB using a mix of SATA drive sizes. This is usually equivalent to 10 to 12 general file servers. While this pales in comparison to enterprise disk arrays with hundreds of terabytes of Fibre Channel storage, disk arrays aimed at SMBs provide plenty of storage for the databases, media and documents needed for day-to-day small business operation. SMB disk arrays are modular, so it should be easy to expand capacity by adding more "boxes" to the LAN or iSCSI SAN.
Management simplicity is important because most SMBs lack the expertise needed to integrate, configure and manage storage systems. The management tools that accompany SMB disk arrays are often wizard-driven and can support multiple boxes as disk arrays get added. Disk array management tasks should also be nondisruptive -- storage adminisrators should be able to add or replace drives without shutting down the disk array or disabling applications. SMB users can also expect wizard-driven thin provisioning, creating a pool of storage space that applications can use as their storage needs grow.
SMB disk array data protectionMost SMB disk arrays include three types of data protection: RAID, snapshots and replication. RAID provides direct data protection for each disk. For example, mirroring stores data on one disk but duplicates that content to a second disk. If one disk fails, the mirrored disk takes over without interruption until the failed disk is replaced.
Other types of RAID protect groups of disks and can actually reconstruct data on the failed drive using parity data. In fact, RAID 6, also known as dual-parity RAID, can guard a RAID group against two simultaneous disk failures. The problem with RAID is that not all disks are available for data storage, and some disks must be committed to storing parity data.
Snapshots periodically capture the system state and save that data to storage elsewhere on the array or in another storage system. Disk-to-disk snapshots are fast -- they can copy terabytes of data in just a few minutes. This results in a short backup window. In addition, the system can track hundreds of snapshots over time, allowing users to retrieve old or changed files. For example, the StoreVault S300 can support up to 255 snapshots per volume. When the snapshot limit is reached, the oldest snapshots "age out" to make room for newer snapshots.
Replication, once the domain of high-end enterprise arrays, allows SMB users to move data across a WAN to remote locations where it can be protected against fires, floods and other disasters.
SMB disk array connectivity and availabilitySMB disk arrays typically connect to the user LAN using Ethernet ports. More disk arrays are incorporating iSCSI target capabilities, allowing the same disk array to transfer file and block data simultaneously across the same Ethernet interface. An iSCSI SAN fabric can be beneficial when the business must support block-based applications, such as databases or other transaction-oriented tasks.
Today's SMB disk arrays provide multiple Ethernet ports for performance and availability. For example, an array might offer four 1 Gbps Ethernet ports, improving performance through port aggregation. Multiple ports allow data to be exchanged faster and can balance the traffic load to ease congestion. The ports can also be arranged to support failover -- if one port fails, traffic is redirected through the remaining port(s). This ensures that the storage system is always available to the LAN or SAN fabric in the event of a failure.
SMB cost issuesMany of the features now standard in SMB disk arrays were once considered expensive options in enterprise-class storage systems. These features are now commonly available in storage systems that dip below the $3,000 mark. However, like enterprise users, SMB users must also look beyond the initial price tag to consider software licensing, service/maintenance agreements and other add-on costs that can recur annually.
30 Nov 2007