Viewing SCSI errors..

[Eric Anderson]

Jerlique Bahn wrote:
>>> I've added a tape drive to my server and the drive only seems to work at
>>> 2MBps.  The drive should be doing about 24MBps. The tape is a DELL 110T
>> LTO2
>>> which runs at about 86Gb/hr.
>>>
>>> I am trying to diagnose where my problems could lie, and was wondering
>> how I
>>> could see if there are any errors in the communication between the tape
>> and
>>> the scsi card (320Mbps). I'm quite confident the speed issue is related
>> to
>>> the tape drive or the scsi chain.
>>>
>>> Your suggestions welcomed.
>>
>> How did you measure the 2MBps number?
> 
> With iostat, eg 
> 
> # iostat 5
>       tty           amrd0            amrd1              sa0             cpu
>  tin tout  KB/t tps  MB/s   KB/t tps  MB/s   KB/t tps  MB/s  us ni sy in id
>    0   12 57.81   2  0.13  53.21   6  0.32  31.99  24  0.76   0  0  1  0 99
>    0   46  8.00   0  0.00   0.00   0  0.00  32.00  88  2.74   0  0  0  0 100
>    0   16  0.00   0  0.00  16.00   0  0.01  32.00  87  2.73   0  0  1  0 99
>    0   15  0.00   0  0.00   0.00   0  0.00  32.00  88  2.74   0  0  0  0 100
>    0   16  0.00   0  0.00   0.00   0  0.00  32.00  88  2.74   0  0  0  0 99
> 
> JB


What tool was writing to the tape?  Most of the time, tapes require you 
to stream the data evenly to it, to avoid 'shoe shining'.  I usually use 
something like:

tar -b 256 ...
or use a buffering tool to buffer the data going to the tape device (use 
a pipe).

You might try some various bs= arguments to dd, to see if you can get 
the throughput up.

Eric


-- 
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Eric Anderson        Sr. Systems Administrator        Centaur Technology
Anything that works is better than anything that doesn't.
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