HP StorageWorks 4000/6000/8000 .HP StorageWorks SAN Design Reference Guide, Pa - Page 393

RAID level For database volumes, the choice of RAID protection on the disk arrays is a trade-off between maximum storage and performance. For the same number of disk spindles, RAID 5 provides data protection and maximum storage, and RAID 1+0 provides the best performance but with less storage. Six spindles in a RAID 1+0 array provide greater performance than six spindles in a RAID 5 array for a given number of Exchange mailboxes. RAID 1+0 is preferred for the database volume. Using six 36 GB drives in a RAID 1+0 array provides ample storage and performance for a thousand 100 MB mailboxes. Designing storage arrays with the large disk drives (146 GB or larger) requires caution. Although a few large disks can provide the required amount of database storage, the reduced spindle count will decrease I/O performance. Write-back caching Write-back caching increases performance for transaction logs on the server array and for databases on the storage array. On array controllers with battery-backed write cache (such as the Smart Array 5i Plus and later) the write-cache percentage should be set to 100%. Recommendations HP recommends that you: • Place the Exchange log files and database files on separate RAID 1+0 RAIDsets. • Place the Exchange log files on Exchange server disks. • Use hardware RAID controllers with write-back caching. Supported load with Exchange The performance required by the average email user determines the storage design. The average load is multiplied by the number of users to find the storage requirement. Conversely, the capabilities of an existing system can determine the maximum number of users. To calculate the average I/O per user in an Exchange environment, the PERFMON object's disk-transfers-per-second value is divided by the number of active connections. The storage capacity calculated from the average I/O needs an additional safety factor to maintain performance during peak periods. In practice, the maximum number of users is less than the calculated value when: • Users increase the size of their mailboxes. • Services such as antivirus scanners or content indexers are added to the Exchange server. A medium-sized user profile provides a 60 MB mailbox, and a large profile provides a 100 MB mailbox. Larger mailboxes affect both storage sizing and performance, and are disproportionately more difficult for Exchange to manage. Sample iSCSI NAS Microsoft Exchange Server 2003 configuration This section summarizes results from an HP-tested iSCSI NAS configuration. Details of this test are available at http://storage.corp.hp.com/Document_Storage/whitepapers/new_library/ 5982-9399EN_Exchange_2003_HP_iSCSI_and_WSS_NAS_WP.pdf. SAN Design Reference Guide 393