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Old 05-14-2008, 01:43 PM   #1
Tyler_H72
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Question LTO2 Backup Too Slow


I am working on a server that I did not personally set up, so I am not aware of EVERYTHING that has been done to it, but I have been working with this particular issue for several days now and am fairly well acquainted with it. I am running SuSE Enterprise Server 10. My SCSI card is an Adaptec 39320A and it is connected only to my LTO2 tape drive, which has termination enabled using the jumpers.
My problem is that I am getting anywhere from 2-3MB/s, when the documentation says that it can handle 32. I realize that I can't realistically expect those speeds, but I am hoping that I can get somewhere around 20MB/s. I noticed that the activity LED on the drive was indicating that it would write for a short time, then wait for a about 3 times as long, then write again, and on and on like this. I messed with the buffer, and it seems to be writing continuously now, but I'm still not getting any better speed. I am not using any backup software- simply the tar command. The syntax that I am using is as follows:
tar cf /dev/st0 [filename]
The file that I am using for testing purposes is approximately 15GB. It is made up of many small files, which I realize will cause slower speeds, but it shouldn't be taking an hour and 20 minutes to write, no matter how small the files are. I had been slightly suspicious that I was losing large amounts of time to the tar command, so (more to rule it out than for any other purpose) I tried just using tar on the same file and writing to a location on the disk- I got somewhere around 21MB/s. I also changed the starting point of the throughput negotiations on my SCSI controller from 320 to 160, following the advice found in another thread that helped someone with a very similar problem on an LTO3. This did not help me at all. I am completely at a loss as to where to turn next. Any help would be greatly appreciated. Thanks!

Last edited by Tyler_H72; 05-14-2008 at 01:49 PM.
 
Old 05-14-2008, 06:58 PM   #2
choogendyk
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You've told a little about your hardware, but not enough. The off and on writing would indicate that it was shoe-shining -- that is, if you can't drive it fast enough, it has to stop, backup, reposition, and prepare to continue writing. That drastically slows it down when it is already slow. If you can maintain the data throughput to keep it writing, then it will maintain its speed.

So, where is the slowup? What is the drive you are pulling from? What is the hardware in general? What else is the server doing? What if you tried just a dd, which wouldn't mess with any processing, but just shove data at it? Or try one of the tape testing utilities, such as amtapetype, which comes with amanda (see http://www.linuxquestions.org/bookmarks/tags/backup). That will drive it hard and tell you what your setup can do.

Anytime you are dealing with driving LTO, you have to look at your entire system and the data path in terms of hardware paths and speeds.
 
Old 05-14-2008, 11:44 PM   #3
Tyler_H72
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Thanks very much for the help! I actually figured it out on my own, right before I talked to you. Turns out that I had messed up with the SCSI Select utility- I had accidentally changed the throughput on ID 13 instead of 6... I changed that and it worked perfectly. I really appreciate the advice though!
 
  


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