Tape drive slowing down?

[Jesse Keller]

I've got a Surestore 1/9 with an LTO-3 drive. I used to get better than 3,000 MB/s on my backups, but lately, I'm getting more like 2,000.

What could cause a slowdown like this -- and what can I do to fix it?

Thanks!

[meloni]

LTO3 may work more than 10 time the speed you are reaching.
Usualy the low throughput is due to the source of the data, not due to the tape drive

you can use LTT with the device and the system test in order to identify the problem

[Jesse Keller]

Thanks for the tip. What's a "good" read speed?

I've just run some tests using LTT, and here's what I'm seeing:

15k RPM mirror:

4874 MB read (31112 files) in 180 seconds with rate 27 MB/sec.


4 x 7200 RPM RAID 5:

5204 MB read (8420 files) in 180 seconds with rate 28 MB/sec.

[meloni]

I do not have a"good" figure for a data read speed, this depend of a lots of things, the raid model, the disk speed as you wrote, but also depend of the defragmentation of the disk, the block size, the kind of partition, etc...
Also 180 seconds is a bit low to have a good view, as you may have some interferences from the disk or controller cache.

what you should do is to compare the speed you got reading the source of the data with the result of the "device performance test", The lowest value is where you should work on to fix the problem

the "device performance test" should indicate the max throughput you can reach from the host to the tape drive, and this value of the test should be similar to the max troughput of the tape drive.

[dueni]

hoi

Another hint:
If you are doing file backup, small files can give a poor performance! (Independent of the operating system!) Use LTT to read out the data of your backup path.

And something to consider:
The LTO drives need a minimum feed speed. If that feed speed (speed of the coming data) is to low, the tape has to stop because of missing data to write, rewind back, write until data is missing, rewind back,â ¦ Thatâ s called shoe shine effect.
For LTO3/Ultrium 960 drive this minimum speed it 1/3 of the max speed:
80MB/s divided by 3 = 27MB/s
This is due the Adaptive Tape Speed of the HP LTO drives; the speed of the tape drive can be adapted to 1/3 of the max speed.

Those 27MB/s has to be delivered at least, or the drive speed gets much lower in case of the shoe shine effect!

An example for LTO3: If the data could be delivered with 15MB/s, then the backup speed is even worse, it could be at about 5 to 10MB/s.

LTO1 (Ultrium 230) min speed 5MB/s
LTO2 (Ultrium 460) min speed 10MB/s
LTO3 (Ultrium 960) min speed 27MB/s
LTO4 (Ultrium 1840) min speed 40MB/s
Better would be at least 20% more than the min speed!

In your example itâ s really bad. But Iâ m not sure that an LTO3 is in your Autoloader. Is it not only a LTO1? Then the max speed is 15MB/s and your min speed should be 5MB/s.

regards

dueni