Fine-tune storage networks


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Performance tips for arrays and tape drives
Fibre Channel (FC) storage arrays
  • Allow storage vendors to size the cache on high-end arrays
  • Turn on and configure the read-and-write cache on midrange arrays
  • Partition the cache to certain applications if the storage array supports it
  • Leave the FC ports at autonegotiate
  • Use FC drives in RAID 5 configurations for most high-performance applications
  • Use serial ATA drives in RAID 6 configurations for low-performance or backup jobs

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FC tape drives
  • If possible, use disk or a virtual tape library as the initial backup target
  • Use tape drives with memory buffers
  • Reserve tape drives for certain applications to simplify tuning
  • Upgrade to tape drives that auto-adjust to the flow of incoming data

FC directors
While configuring and tuning FC HBAs often occurs during the initial install, FC directors require more ongoing changes as the SAN evolves. Application, server and storage growth, backup configuration changes and connecting SAN islands creates a more dynamic environment for FC directors. Though FC directors usually provide ample bandwidth and throughput, performance may deteriorate as changes occur because:

  • Multiple applications are accessing the same storage port
  • A zone includes too many server ports
  • Server placement is on edge and core SAN switches
To reduce costs, many storage managers assign multiple server HBA ports to the same storage HBA port--a common practice to minimize the number of ports used on the SAN switch. But when the performance requirements of one or several applications begin to grow, port oversubscription turns into port congestion, which impacts the operation of other servers accessing storage on that port.

Resolving this issue requires access to the director zoning information and possibly a performance-measurement tool. The director management software will identify all of the HBAs zoned to a specific storage port and which port they're plugged into on the FC SAN. With the ports identified, you can determine which application is the culprit and take corrective action.

If an informal review doesn't immediately reveal the offending application, each FC director vendor offers tools that capture and monitor information from specific FC ports. Brocade's SAN Health, Fabric Watch, Fabric Manager and Advanced Performance Monitoring tools can help identify the problem. SAN Health is a free download from Brocade's Web site and can be used on any vendor's FC director to take a performance sample. Brocade's Fabric Watch product can be configured to send an alarm if a port exceeds a certain performance threshold, while its Fabric Manager tool provides historical performance data. The Advanced Performance Monitor tool provides more advanced diagnostics on how FC traffic moves through the fabric and how the SAN is designed; it only needs to be used if the other tools can't pinpoint the performance problem.

This was first published in April 2006

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