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Hersteller: Adaptec Dateigröße: 768.1 kb Dateiname: SAS_HostRAID_Installation_and_Users_Guide_10-06.pdf Unterrichtssprache:

The ability to respond to multiple data requests provides not only an increase in throughput, but also a decrease in response time. The combination of parallel transfers and simultaneous responses to multiple requests enables disk arrays to provide a high level of performance in network environments. Understanding Drive Segments A drive segment is a disk drive or portion of a disk drive that is used to create an array. A disk drive can include both RAID segments (segments that are part of an array) and available segments. Each segment can be part of only one logical device at a time. If a disk drive is not part of any logical device, the entire disk is an available segment. Stripe-unit Size With RAID technology, data is striped across an array of physical drives. This data-distribution scheme complements the way the operating system requests data. The granularity at which data is stored on one drive of the array before subsequent data is stored on the next drive of the array is called the stripe-unit size. You can set the stripe-unit size to 16, 32, or 64 KB. You can maximize the performance of your HostRAID controller by setting the stripe-unit size to a value that is close to the size of the system I/O requests. For example, performance in transaction-based environments, which typically involve large blocks of data, might be optimal when the stripe-unit size is set to 32 or 64 KB. However, performance in file and print environments, which typically involve multiple small blocks of data, might be optimal when the stripe-unit size is set to 16 KB. The collection of stripe units, from the first drive of the array to the last drive of the array, is called a stripe. Selecting a RAID Level and Tuning Performance Disk arrays are used to improve performance and reliability. The amount of improvement depends on the application programs that you run on the server and the RAID levels that you assign to the logical drives. Each RAID level provides different levels of fault-tolerance (data redundancy), utilization of physical drive capacity, and read and write performance. In addition, the RAID levels differ in regard to the minimum and maximum number of physical drives that are supported. Appendix B: Understanding RAID . 60 Appendix B: Understanding RAID . 60 RAID Level Data Redundancy Physical Drive Capacity Utilization Read Performance Write Performance Built-In Spare Drive Min Number of Drives Max Number of Drives 0 No 100% Superior Superior No 1 4 1 Yes 50% Very high Very high No 2 2 10 Yes 50% Very high Very high No 4 4 Physical drive utilization, read performance, and write performance depend on the number of drives in the array. Generally, the more drives in the array, the better the performance. RAID 0 (Non-RAID Arrays) An array with RAID 0 includes two or more disk drives (maximum twelve) and provides data striping, where data is distributed evenly across the disk drives in equal-sized sections. RAID 0 arrays do not maintain redundant data, so they offer no data protection. However, compared to an equal-sized group of independent disks, a RAID 0 array provides improved I/O performance. Drive segment size is limited to the size of the smallest disk drive in the array. For instance, an array with two 250 GB disk drives and two 400 GB disk drives can create a RAID 0 drive segment of 250 GB, for a total of 1000 GB for the volume, as shown in the following figure. Drive Segment Size (Smallest Disk Drive) Disk Drive 1 250 GB Disk Drive 2 Disk Drive 1 Disk Drive 2 Disk Drive 3 Disk Drive 3 250 GB 400 GB 400 GB Unused Space: 150 GB Disk Drive 4 Disk Drive 4 1 2 3 4 Not Used Not Used 5 1000 999 998 997 6 7 ... 8 ... ... ... Unused Space: 150 GB Disk Drives in Logical Drive RAID 0 Logical Drive = 1000 GB Appendix B: Understanding RAID . 61 Appendix B: Understanding RAID . 61 A RAID 1 array is built from two disk drives, where one disk drive is a mirror of the other (the same data is stored on each disk drive). Compared to independent disk drives, RAID 1 arrays provide improved performance, with twice the read rate and an equal write rate of single disks. However, capacity is only 50 percent of independent disk drives. If the RAID 1 array is built from different-sized disk drives, the free space, drive segment size is the size of the smaller disk drive, as shown in the following figure. 250 GB Drive Segment Size (Smaller Disk Drive) Disk Drive 1 Disk Drive 1 Disk Drive 2 Disk Drive 2 400 GB Unused Space: 150 GB Not Used 1 – 250 1 – 250 Disk Drives in Logical Drive RAID 1 Logical Drive = 250 GB RAID 10 Arrays A RAID 10 array is built from two or more equal-sized RAID 1 arrays. Adaptec RAID controllers support a maximum number of 48 disk drives in a RAID 10 array. Data in a RAID 10 array is both striped and mirrored. Mirroring provides data protection, and striping improves performance. Drive segment size is limited to the size of the smallest disk drive in the array. For instance, an array with two 250 GB disk drives an...

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