System reliability is a vital component in Storage Area Network (SAN) design that keeps your production environment operating and avoids data loss and downtime. But since SANs are built using both mechanical and electronic parts, component failures due to usage, environmental factors, or manufacturing defects are not uncommon. Even in completely redundant systems, controllers can fail, fans can stop operating, power supplies can burn out, and disk drives can degrade or fail.
COFFEE BREAK
BUILDING A HIGHLY RELIABLE SAN
Focusing on the reliability of System reliability is a vital component in Storage Area Network (SAN) design thatindividual components often keeps your production environment operating and avoids data loss and downtime. Butresults in greater expense since SANs are built using both mechanical and electronic parts, component failureswith no improvement in due to usage, environmental factors, or manufacturing defects are not uncommon.system reliability. Even in completely redundant systems, controllers can fail, fans can stop operating,power supplies can burn out, and disk drives can degrade or fail.
To eliminate downtime, IT managers should focus on total system design and how com-ponents work together to deliver reliability. A common mistake is to evaluate individualcomponent reliability alone - you can "miss the forest for the trees" and significantlyincrease expenses with no improvement in overall system reliability.SATA vs. FC/SCSI disk drivereliability differences are SYSTEM DESIGN TRUMPS COMPONENT RATINGSimmaterial to system reliability While SAN component reliability ratings are of interest, system reliability is establishedwhen comparing well as a result of all these components working together. For example, a server with onedesigned storage systems. direct-attached disk is only as reliable as that disk; the server's electronics reliability rating may be very high, but if the disk fails, the system fails. However, configure twointernal disks with RAID, and reliability improves dramatically; a disk failure does notimpact system operation because of the "designed-in" redundancy.
Some storage vendors want SAN buyers to focus on individual disk drive reliability ratings, but good system design and RAID implementations render these statisticsessentially moot. Individual disk drives are commonly assessed using the statistical calculations of Mean Time to Failure (MTTF), measured in hours, and storage arrays areassessed using Mean Time to Data Loss (MTTDL), measured in years. SATA drives currently test at 600,000 to more than 1 M hours MTTF at 100% duty cycle* (and offera price/performance option that FC or SCSI disks cannot match). Consider a 14-driveRAID system with disk drives rated at 600,000 hours MTTF. For that system, the lowest MTTDL - the storage administrator's key concern - in a RAID 50 environmentis 70,000 years, and in a RAID 10 environment is 360,000 years.
In addition, reliability ratings should be compared in the context of capacity. FC andSCSI disk drives may be rated with higher reliability (800,000 - 1.5 M hours MTTF) thanSATA drives (600,000 - 1 M hours MTTF). However, since FC and SCSI drives offerless capacity than SATA drives, it takes more disks to deliver the same capacity, result-ing in higher failure rates per TB. When you measure overall . Redundant Data Paths - All connections from servers tosystem reliability in terms of capacity, FC and SCSI drives storage should be redundant.offer less reliability per TB than SATA. . Automatic Load Balancing - Arrays that automatically loadbalance data across all available disks improve reliability byBEST PRACTICE SYSTEM DESIGN lowering the duty cycle on each disk, as well as improvingTo ensure maximum uptime IT managers must properly config- total system performance and utilization.ure the SAN environment, using storage arrays specificallydesigned for full redundancy, online servicing without disruption . Continuous Self-monitoring and Self-correction - Storageor compromise of data protection, and automated management arrays should provide continuous monitoring of all compo-that minimizes disk workloads. Best practices include: nents including proactively testing disks in production.. Interoperable Infrastructure - SAN technology should beeasily deployed and interoperable. This minimizes disrup-tions caused by incompatible devices.. Redundant System Architecture - All components shouldbe fully redundant, online serviceable, hot swappable -disk drives, fans, power supplies, controllers, and networkinterfaces.** RAID caches improve system performanceand must be protected via mirroring between controllers.Servicing a system should not compromise data protectionsuch as RAID.. Advanced Chassis Design - Chassis should be designedfor advanced cooling and vibration da... [download for more]
