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I am testing out a new Quantum Ultrium 8 Tape and Drive. I see the listed maximum uncompressed and compressed data rate, respectively, are 360 MB/s and 900 MB/s. How can I observe/demonstrate this level of performance most simply? I was trying this:

dd if=/dev/urandom of=/dev/shm/random-data bs=64M count=16

end=$((SECONDS+60))
while [[ $SECONDS -lt $end ]]; do
    dd if=/dev/shm/random-data of=/dev/nst0 bs=1M count=1024
done

Chunk of the output:

1024+0 records in
1024+0 records out
1073741824 bytes (1.1 GB) copied, 7.66494 s, 140 MB/s
1024+0 records in
1024+0 records out
1073741824 bytes (1.1 GB) copied, 8.10491 s, 132 MB/s
...

I got an average speed of 126 MB/s. When I tried to test the compressed data rate, by filling up another file in /dev/shm/ with 1GB from /dev/zero and doing the same loop, I got an average of 282 MB/s.

Is there another simple way to observe/demonstrate the expected data rates (or at least just the uncompressed speed)? What is causing the limitation I'm observing?

Levi Uzodike
  • 221

1 Answers1

1

You can observe transfer rate with tapestat Linux command. Here is a man page.

The tapestat command is used for monitoring the activity of tape drives connected to a system.

The tapestat report provides statistics for each tape drive connected to the system. The following data are displayed: ... kB_read/s | MB_read/s The amount of data read expressed in kilobytes (by default or if option -k used) or megabytes (if option -m used) per second averaged over the interval.

For example, I would firstly create dummy data (e.g., 10GB) with /dev/urandom and store it under disk system which is faster enough than LTO's maximum transfer rate. In this specific case, disk's transfer rate shall be >360MB/sec. I would recommend SSD or tmpfs to avoid any bottleneck. Then, write the dummy data to LTO-7 media with tar, something like tar -cvf /dev/st0 dummy_data. Just after starting write process, you should invoke tapestat 1, which will show averaged transfer rate every second.

If output is less than 360MB/sec, there should be a bottleneck in your system. It can be due to SAS card speed, disk speed, internal bus speed, or even your tape drive/media is about to fail.

Kevin Nakamoto
  • 96