1. Drive positioning
Be sure to consider the position of drives within the storage system and carefully follow manufacturer recommendations. Because of differences in rotational speed between SAS and SATA disk drives, the vibration from a high-performing SAS drive can negatively impact an adjacent, slower-spinning SATA drive in the same column, causing the SATA drive to fail. Overland Storage, for one, recommends that SAS and SATA drives be placed in separate columns within the company's Ultamus RAID 1200 if both SAS and SATA are used.
2. Failover support
Take into consideration whether the applications your customer plans to use with the storage system are mission-critical. For instance, backup and archiving applications generally require lower levels of storage system availability, while databases and email require storage systems with almost constant availability. Some storage systems don't support failover between controllers; others are available only in active-passive configurations, wherein one controller is dormant while the other handles all of the I/O traffic. These factors come into play when recommending storage systems so they an application's availability, failover and performance requirements.
3. High-level RAID
Ensure that any storage system with high-capacity SAS or SATA disk drives minimally provides an advanced RAID feature and possibly even offers some ways for users to conserve energy. Most mixed SAS/SATA systems now support RAID 6, which uses two disks in a RAID array group for data protection. This protects users against the possibility of data loss should a second disk fail before the rebuild of a first disk failure is complete. This is an increasingly likely scenario for both SAS and SATA drives due to the increasing capacity on both of these disk drives.
4. Going "green"
Consider "green" features that might entice a prospective customer to make a purchase. While such capabilities have been slow to make their way into products, expect the pace to pick up. NEC's new D-Series is unique among mixed SAS/SATA storage systems as it scales from the entry-level D1-10, with two controllers and three disk drives, to the D8-1040, with 16 controllers and 1,536 disk drives. As users add more data to it, using its MAID technology, they can configure it to spin down unused disk drives during specific times of the day to conserve power.
Beware that the firmware on SATA disk drives is not as robust as the firmware used on SAS disk drives. Firmware on SATA drives is more apt to report drive failures, even when the SATA disk drive has not failed or the disk drive takes multiple seconds to perform a read or a write. While these false negatives are inconvenient for noncritical applications, they can appear at the most inconvenient times when used with critical applications, creating a negative impression of the storage system and the VAR who recommended it.
Mixed SAS and SATA storage systems are poised to become a major part of the storage landscape in 2008, especially for SMBs who initially stand to benefit the most from this new technology. Understanding these issues before you take on and offer mixed SAS/SATA storage will help increase your profitability as well as minimize the issues you have supporting them once they are installed at your client site.
About the author
Jerome M. Wendt is the founder and lead analyst of The Datacenter Infrastructure Group, an independent analyst and consulting firm that helps users evaluate the different storage technologies on the market and make the right storage decision for their organization.
This was first published in October 2007