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A final concern that users need to address with HSM products is how the central server communicates with client servers over the network (see "Best practices for using HSM software," below). Products like IBM's TSM for Space Management and HSM for Windows, and SGI's InfiniteStorage DMF use a proprietary protocol to communicate between server and client. Although this may require users to open additional ports on their network, it lets users secure communications between the server and clients. Products from CA, CommVault Inc. and Symantec use more common protocols like CIFS, FTP or NFS to communicate; this may present security risks in some environments because they don't offer options to secure transmitted data.
Best practices for using HSM software
There are no hard-and-fast rules on how to best use hierarchical storage management (HSM) software, but the following tips address some of the most important considerations for selecting, installing and using an HSM product.
Classify your data. This usually requires the use of a host-based, file-level storage resource management (SRM) tool that identifies and classifies files. Reports will break files down by attributes such as file size, usage patterns,
| last-accessed or modified date, and owner.
Implement HSM software as part of a technology refresh. Rather than trying to justify HSM software as a standalone purchase, wait until more storage is needed. Then purchase HSM software as an alternative to buying more high-end storage as it will allow you to migrate files to lower cost storage systems.
Identify what files you don't want migrated. Database files, libraries and executables are examples of files that may not be accessed very often but need to stay on primary disk. Some HSM software packages, like CA Inc.'s BrightStor HSM, include default policies that prevent these files from being accidentally migrated.
Choose an HSM software package recognized by your backup software. Your backup software needs to recognize stub files created by the HSM software so that when backups occur, the backup software backs up only stub files or inodes and doesn't recall migrated files from tape or optical media.
Determine if you want to manage migrated files centrally or locally. Products such as EMC Corp.'s DiskXtender and CA's BrightStor HSM don't provide a central catalog or database; they manage the location of all file migrations on a local database on each host. This eliminates the requirement to communicate with a central server and create a high-availability configuration for the central server. Conversely, centrally managed HSM products, such as IBM Corp.'s Tivoli Storage Manager for Space Management and HSM for Windows, use a central server that eliminates the need for admins to log on to each server to manage the HSM software. It also lets admins create global policies that can be applied to all managed hosts.
Consider the dependencies of HSM software. Most software products have some prerequisites, including the need for specific backup software or versions of file systems. If not already in place, these can add to the cost and difficulty of the installation and configuration of the HSM software.
What operating systems does the HSM software support? The number of OSes supported by HSM software products varies, and most vendors offer different HSM software products for Unix and Windows because of differences in the file systems of these operating systems.
This was first published in November 2006