PREVIOUSLY: About multi-protocol arrays
Is there a difference between multiprotocol and single-protocol arrays with regards to redundancy and failure predictability? Simply put, multiprotocol arrays can't match the performance and reliability of high-end, single-protocol arrays. "There are a number of applications that require a level of availability only provided by high-end SAN arrays like HDS Universal Storage Platformor EMC Symmetrix, mostly because of their ability to predict the performance impact in case a node fails," says Chris Bennett, NetApp's VP of core systems.
This level of high availability can be extended to file-based storage access by front-ending an EMC Symmetrix or HDS USP with a NAS gateway; for example EMC's Celerra NAS gateway can be paired with a Symmetrix. Not having its own NAS gateway, HDS offers a NAS blade for its TagmaStore USP that enables access to USP storage via file-system protocols.
To increase the availability in arrays that support file- and block-based protocols through a single controller, nodes are often clustered; if a node fails, another node takes over its workload. Clusters are available in active-active and active-passive configurations. With an active-active cluster configuration, it's crucial to design the cluster to cope with the reduced processing power in case of a node failure. The cluster configuration may also impact the amount of usable storage, a fact painfully experienced by Chalkley Matlack, senior network administrator at doeLegal, who replaced his EMC Celerra NS500 array with a Reldata. storage system. "We weren't able to move the NS500 beyond 16TB without switching from an active-active to an active-passive configuration, giving up redundancy," laments Matlack.
Cluster options are available at the higher end of the performance and price product spectrum from such companies as EMC, Microsoft, NetApp and Pillar Data Systems. Multiprotocol array clusters are the way to go in environments with 24/7/365 uptime requirements. "Availability was our primary concern when we chose NetApp 3000 series clustered arrays for all of our locations," explains Michael Israel, senior VP of information services at theme park operator Six Flags.
Storage management
Managing the storage of multiprotocol arrays is more challenging than managing FC-only arrays, mostly due to the limited support of NAS protocols by storage management apps and storage standards. "SMI-S has been targeting the SAN market and paid little attention to file-system protocols," says Sean Derrington, Symantec's director of storage management.
Storage resource management (SRM) vendors have overcome this hurdle by directly integrating their suites with arrays from leading storage vendors, with NetApp enjoying the most extensive support among arrays supporting both NAS and SAN. For instance, Symantec CommandCentral 5.0 has been integrated with NetApp filers down to the file level across multiple filers and multiple locations. "We're able to monitor performance and capacity across multiple filers and locations using a combination of SMI-S and Data Ontap APIs, a capability currently only available for Network Appliance filers," explains Derrington.
Similarly, vendors that offer both multiprotocol arrays and SRM apps such EMC ControlCenter and HP Storage Essentials typically provide tighter integration and more advanced management options for their own multiprotocol arrays.
"For NetApp filers and the HP StorageWorks All-in-One Storage System, we offer a Storage Essentials agent that extends the full SRM capabilities to file-system protocols," says HP's Dean Schneider, marketing planning manager for Storage Essentials.
Array features
The features in some multiprotocol arrays are on par with, and in some cases ahead of, single-protocol arrays. Snapshot and replication have become standard features in arrays supporting NAS and SAN. While all vendors support replication, they differ in their implementation of it. Does the array support synchronous and asynchronous replication? Can replication be performed at a file and block level, or is it limited to one of the two protocols? NetApp and Pillar Data Systems, for example, support synchronous and asynchronous replication, and storage administrators have a choice of file- and volume-based replication.
Multiprotocol arrays provide a wider range of backup options than block-based arrays. Besides snapshot and replication, users can directly back up data through CIFS and NFS file-system protocols without going through another server. Moreover, the majority of multiprotocol arrays - Windows Storage Server excluded - support the Network Data Management Protocol (NDMP), which is optimised for backup and eliminates the need for installing a backup agent on the storage system. Being Windows based, the lack of NDMP support in Windows Storage Server isn't much of an issue, as most Windows Server 2003-compatible backup applications will also run on Windows Storage Server.
Thin provisioning is becoming increasingly important and is available in multiprotocol arrays from EMC, HDS and NetApp. Deduplication is another feature making inroads. While a few vendors have some level of deduplication, NetApp is currently the only multiprotocol array vendor offering a deduplication option for all of its filers.
Price
If both file- and block-based protocols are required, procuring a multiprotocol array or NAS gateway is significantly less expensive than buying two arrays. "As a rule of thumb, you can add about 10% of the array price for additional protocols," says NetApp's Bennett.
In general, arrays from leading storage vendors like NetApp and EMC include only a limited number of features in the base price, and extra features and protocols have to be bought separately. Some customers are repelled by having to pay for features they expected to be part of the base price and are driven to array vendors with a more inclusive pricing model.
NEXT: Multi-protocol products