Compaq ProLiant 6500 DSS Sizing and Tuning of Oracle8 for Windows NT on Compaq - Page 20

Page 18 DSS Sizing and Tuning of Oracle8 for Windows NT on Compaq Servers other drives. Log drives should be placed on a RAID-1 drive, so that no log files are lost in the case of a single disk failure. Array Controllers The Compaq SMART Array Controller is preferable to standard SCSI controllers. The following are benefits achieved when using the Compaq SMART Array Controllers. This information is specific to the Compaq SMART-2/P and SMART-2DH controllers. • Allows for up to 14 disks to be configured in the system as one or more logical drives. When multiple disks are collected into a single array, any logical drives created on that array will have their data striped across all of the disks. This will more evenly distribute the data across the disk spindles so that your I/O load will be more balanced on them. This works really well for random I/O loads or for sequential loads where you do not have more sequential streams accessing the data than you have defined logical drives on which the data coexists. For example, if you spread your table across four logical drives, to maintain sequential streams, you should keep your degree of parallelism on that table to four or less. Each logical drive will then be sequentially scanned, which results in a sequential scan of the physical disks. • Multiple logical drives can be configured on each disk or array of disks. The maximum number of logical drives per single controller is 32. In a DSS system, you will want only one logical drive per disk. • The accelerator cache can be configured as either read-ahead cache or write-posting cache or varying degrees of both. The memory for the accelerator is either 4MB or 16MB, depending upon the version of the controller board. The memory can be configured at 100/0 percent, 75/25 percent, 50/50 percent, 25/75 percent or 0/100 percent for the amounts of memory that will be reserved for the read-ahead/write-posting functionality of the accelerator. The configuration you choose will primarily depend upon the amount of writes to your database. • Controller provided RAID levels - Defining RAID levels at the controller versus software RAID on Windows NT relieves system processor overhead for maintaining RAID. I/O Limits In a DSS system, it is optimal to tune for most data access to be sequential for better data throughput. When multiple processes are accessing a disk concurrently, it is important not to overload each individual disk with random I/O's. The following are recommended I/O limits for Compaq 4.3-Gigabyte Ultra and 1-inch and 10K RPM 9.1-Gigabyte drives. For 16K block size, Compaq recommends that random I/O's not exceed 60 I/O's per second per drive for the 4.3Gigabyte Ultra drives, and 75 I/O's per second per drive for 9.1-Gigabyte drives. While the system is under load, determine the number of I/O's per second to each logical volume using the Performance Monitor. See Figure 10. Then, using the formulas in the Compaq Database Engineering White Paper Configuring Compaq RAID Technology for Database Servers, you can calculate the number of I/O's per physical disk based on the fault tolerance level of that particular logical volume. In the example displayed in Figure 10, there is no fault tolerance on logical NTFS volume G. The average I/O rate is 478.262 I/Os per second. If the drive set consists of seven 4.3-Gigabyte Ultra drives, then the I/O rate per second per drive is 478.262 / 7 = 68.32 I/O's per second per drive. The test purposely flooded the logical drive with I/O's, giving a scenario above the recommended 60 I/O's per second per disk and requiring the possibility of adding more disk drives or rearranging files. If the drive set consists of seven 9.1-Gigabyte drives, then the 68.32 © 1998 Compaq Computer Corporation, All Rights Reserved Doc No ECG156/0398