Veritas NetBackup™ Appliance Capacity Planning and Performance Tuning Guide
- About this Guide
- Section I. Capacity planning
- Analyzing your backup requirements
- Designing your backup system
- Section II. Best Practices
- Section III. Performance tuning
- Section IV. Quick reference to Capacity planning and Performance tuning
- Index
Tape Out operations
Tape Out operation is very resource-intensive operation and requires full rehydration of the backup image.
Performance of the tape out operation is limited by how tape drives handle multiple streams. Unlike restore operations that can benefit from appliance performance with multiple concurrent restore streams, tape drives can handle only one stream per tape drive thus limiting tape out performance.
The following guidelines help to improve the performance of a Tape Out operation from MSDP:
To achieve best results any concurrent operation is discouraged.
Better performance improvements can be achieved if tape out is done after the rebasing operation is complete.
It is very important to stream the data to tape drives on or above the tape drive minimum data rate. If stream throughput drops below the tape drives minimum data rate while tape out operation is in progress, the tape drive will stop writing and will start repositioning tape to the last saved segment while waiting for the new data. This is known as the "shoe shining" effect and will slow down the tape out performance significantly.
Note:
Minimum streamed throughput of tape drives depends on the tape drive model and manufacturer. Generations of LTO 4 tape drives usually have minimum data rates of 40 MB/s (uncompressed data) and 80 MB/s (compressed data). Single MSDP rehydration streams have to perform better than this to prevent slowdown of the tape out performance. Another popular tape drive model is HP LTO5 drive (47 MB/s uncompressed and 94 MB/s for compressed data).
Best possible scenario is to have multiple tape drives receiving multiple streams from appliance MSDP (one stream per drive).
The number of tape drives to use depends on many environment parameters. If tape out restore speed is not satisfactory causing "shoe shining" on the tape drives, it is best to try to reduce the number of tape drives used out for tape gradually until an optimal number of tape drives is found for that particular customer environment.