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8 Performance Considerations for Tape Drives and Libraries
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Random access time or seek time.
Usually measured in milliseconds, seek time is the length of
time a drive's heads take to find a piece of data on the disk. The seek time of a hard disk measures
the amount of time required for the read/write heads to move between tracks on the surface of the
platters. Because hard disks are random access devices, data can be stored on virtually any sector of
the disk. The longer it takes to access that data, the slower the overall throughput of the drive. This
attribute is very significant when a hard drive contains many small files. The smaller the files, the
more "seeks" the drive must make to read or write the file to disk; therefore, disks tend to read or
write very slowly when many small files are being transferred.
Sequential/sustained transfer rates (STR).
STR measures how fast a drive actually reads data from
and writes data to its platters. If the data being backed up is one large contiguous file, the sustained
throughput will be close to the drive's maximum STR. However, in real-world applications, data
becomes more scattered about the platter as data is deleted and written. Defragmenting a hard
drive can help the drive reach its maximum STR.
Buffer (cache).
The buffer is the amount of memory on the drive that holds the most recently
written or stored data. The bigger the buffer, the more data it can hold, resulting in less time
seeking data on the disk.
Hardware RAID Configuration Considerations
General overview of RAID
This section presents an overview of typical RAID configurations and how they affect backup and
restore rates. A RAID array is a set of hard disks that act as a single storage system or LUN. Data can
be potentially transferred through the channel of each hard drive at once, allowing for total
throughput to be a multiple of the total number of drives in the array, minus overhead and any
redundancy as described in the following sections.
In the case of a RAID configuration, the speed of the interface becomes important because the
drives share the bandwidth of the interface. For example, a single Ultra160 drive may only sustain
40 MB/sec. Thus, a five-disk RAID 0 array consisting of the same drive type should be able to
read/write at 200 MB/sec. However, the Ultra160 interface will limit the array to a maximum of
160 MB/sec.
External disk arrays, particularly in SANs, may offer significant levels of cache memory to improve
I/O performance. This cache will greatly improve performance when writing to the array and may
store frequently accessed data to improve read performance. With respect to its impact on tape
performance, the cache will mask most RAID limitations when restoring data to the array or
backing up data from the array. However, backup operations from external arrays with cache may
still feel the impact of RAID configuration limitations because the data still needs to be read from
the disks.
- Performance Considerations 1
- Contents 3
- 4 Contents 4
- Introduction 5
- Hard Drive Performance 7
- General overview of RAID 8
- Drives in Tape Libraries 12
- SAN Configurations 13
- 磁带驱动器和磁带存储库 25
- 主机备份一般注意事项 29
- 确定磁带驱动器的性能 30
- 硬盘驱动器配置一般注意事项 30
- 磁带驱动器和磁带存储库性能注意事项 32
- 在磁带存储库中使用多个驱动器时的一般性能注意事项 36
- 使用存储库光纤信道桥接器进行 38
- 42 磁带驱动器和磁带存储库性能注意事项 42
- 44 磁带驱动器和磁带存储库性能注意事项 44
- 46 磁带驱动器和磁带存储库性能注意事项 46
- 48 磁带驱动器和磁带存储库性能注意事项 48
- Remarques sur 49
- Sommaire 51
- 52 Sommaire 52
- Présentation 53
- Performances des disques durs 56
- Configurations SCSI 61
- Configurations SAN 62
- Terminaison 66
- Hinweise zur 75
- Leistungsoptimierung 75
- 78 Inhalt 78
- Einführung 79
- Festplattenleistung 82
- RAID – Allgemeine Übersicht 83
- SCSI-Konfigurationen 87
- SAN-Konfigurationen 88
- SCSI-Kabelverbindung zum Host 91
- Abschlusswiderstand 92
- FC zu optimieren 99
- Dell™ PowerVault™ システム 101
- テープドライブとライブラリの 101
- パフォーマンスに関する考慮事項 101
- ____________________ 102
- ホストのバックアップに関する一般的な考慮事項 105
- テープドライブとライブラリのパフォーマンスに関する考慮事項 106
- ハードドライブと RAID アレイの構成 107
- ハードドライブのパフォーマンス 108
- ハードウェア RAID 構成に関する考慮事項 109
- 図 1-2 RAID 0 構成の例 110
- 図 1-3 RAID 1 構成の例 111
- 図 1-4 RAID 5 構成の例 112
- テープライブラリで複数のドライブを使用する際のパ 113
- フォーマンスに関する一般的な考慮事項 113
- 図 1-5 ファイバーチャネルリンクの図 114
- 推奨するケーブル設定 117
- ホストへの SCSI ケーブル接続 117
- ファイバーチャネルブリッジへのドライブのケーブル接続 118
- ライブラリ SCSI 119
- 図 1-18 ドライブ 1 台のテープライブラリ 125
- 図 1-19 ドライブ 2 台のテープライブラリ 125
- 테이프 드라이브 127
- 및 라이브러리의 127
- 일반적인 호스트 백업 고려사항 131
- 하드 드라이브 및 RAID 배열 구성 132
- 일반적인 하드 드라이브 구성 고려사항 133
- 하드 드라이브 성능 133
- 하드웨어 RAID 구성 고려사항 134
- 테이프 드라이브 및 라이브러리의 성능 고려사항 138
- 테이프 드라이브 및 라이브러리의 성능 고려사항 143 143
- 드라이브를 Fibre Channel 브릿지에 연결 143
- 144 테이프 드라이브 및 라이브러리의 성능 고려사항 144
- 146 테이프 드라이브 및 라이브러리의 성능 고려사항 146
- 148 테이프 드라이브 및 라이브러리의 성능 고려사항 148
- Consideraciones sobre 151
- 154 Índice 154
- Introducción 155
- Información general de RAID 159
- Configuraciones SCSI 164
- Configuraciones de SAN 165
- Terminador 169
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