ArGest Backup User Guide

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Increasing BRU’s Speed

BRU has a number of options that can, at times, increase the operating speed of the program. These options include using a larger I/O buffer and using double buffering.

Before attempting to tune BRU for optimum performance, you should know the maximum speed of your archive device. On many newer systems, BRU is limited by the speed of the tape drive. If your tape drive is already operating at top speed, it is impossible to adjust BRU’s parameters to make it run faster.

Listed below are maximum native speeds for various types of tape drives:

Drive Type Speed
DDS4 2.5MB/sec
DAT160 6MB/sec
DAT320 12MB/sec
LTO-1 15MB/sec
LTO-2 30MB/sec
LTO-3 60/80MB/sec
LTO-4 80/120MB/sec
LTO-5 150MB/sec

The above speeds are the native throughput for the drives listed. Hardware data compression will increase these values depending upon how well the data compresses. The numbers are based on information gathered from the tape drive manufacturers. This list is meant only as a guide, the actual maximum speed of your tape drive may be different. To obtain the rated maximum speed for your drive, refer to the manufacturer’s specifications.

During the I/O operations, BRU calculates the tape read/write speed and records the value in its execution log, /var/log/bruexeclog. Here is a typical log entry (this would be on a single line in the log):

20010903 04:19:10|4331|root|[L182] wrote 256670 blocks on volume [1], 0:48:59, 174 Kb/sec

In this case, BRU was writing to a 4mm DDS1 drive. It took 2,939 seconds (0:48:59) to write 513340 Kbytes (256670 x 2 Kb/block), so the tape speed is 174 Kb/sec. This is very close to the maximum DDS1 speed of 180 Kb/sec, so it is likely BRU is “tuned” for optimum performance. Any further adjustments would probably be futile.

TUNING HINT #1: Make sure you read or write enough data to get an accurate tape speed measurement. Some types of tape drives (like DATs) take several seconds to load the tape before they actually begin reading or writing. This extra time will skew the speed measurement (the apparent speed will be slower) on small amounts of data. To avoid this problem, run your tape speed tests for two minutes or longer. The longer the test, the more accurate the speed measurement will be.

TUNING HINT #2: Do not use BRU’s compression (-Z option) when tuning for optimum speed. Data compression can be used after you have determined the optimum parameters. If your tape drive supports data compression (hardware compression), it is usually faster than BRU’s compression. If this is the case, BRU’s compression option should not be used.