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Mix SAS/SATA drives for speed or capacity

Ezine

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Single-system DLM
The real challenge and opportunity for mixed SAS and SATA storage systems is the ability to move data between different tiers of disk within a single storage system; higher performing data is placed on SAS drives, while data with more modest performance requirements is put on SATA drives. But to place the data on the right volumes requires administrators to know which ones are SAS volumes and which ones are SATA volumes.

To accomplish this on most SAS and SATA storage systems will require some third-party tool such as TeraCloud Corp.'s TeraCloud Storage Framework (TSF) Lite, which monitors the utilization and growth of data in your environment. As data approaches specified age, capacity or performance thresholds, the tool alerts administrators to these issues.

When these threshold issues occur, administrators will likely still need a way to migrate data from one volume to another within the storage system. Some of the SAS and SATA storage vendors, such as EqualLogic, Hewlett-Packard (HP) Co. and NEC, include replication software to replicate data from one volume to another.

If you need to move individual files, products like CommVault's QiNetix DataMigrator or Silicon Graphics Inc.'s (SGI) InfiniteStorage Data Migration Facility (DMF) allow administrators to set policies that monitor file use and growth, and automatically migrate files to the appropriate tier of back-end disk based on access frequency or file type. This approach

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requires administrators to install host agents, set up policies and administer the products on an ongoing basis, although SGI plans to release an integrated solution that will work with its DMF software and InfiniteStorage 220 storage array in late 2007.

EqualLogic allows users to automate the movement of data from one volume to another on their storage systems, but it only works under the following circumstances:

  • Each PS Series storage array supports only one type of disk drive--SAS or SATA--so to introduce automated tiering of data, you must deploy at least two EqualLogic storage arrays with different types of disk drives.
  • Automated data placement is based on the I/O characteristics of each specific volume. Administrators then set policies or accept the default policy levels so the EqualLogic software automatically moves the volume from one tier of storage to another. This setting is not granular to the file or block level.
  • Both volumes must be in the same storage pool, although these storage pools can cross multiple storage arrays. You can only create up to four storage pools, so if volumes reside in pools outside of those volumes the scope of functionality may be limited.
Mixed SAS/SATA storage systems provide an enticing way for midsized companies to introduce tiered storage into their storage environment at a more attractive price than mixing FC and SATA drives within an array. But buyer beware; if you purchase a SAS/ SATA storage array, strictly follow your vendor's best practices for configuring the disk drives within the array and make sure the vendor has an acceptable course of action to correct any problems that may emerge.

This was first published in July 2007

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