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List:       bacula-users
Subject:    Re: [Bacula-users] Multiplexing multiple jobs to tape
From:       Chris Howells <chris+bacula () chrishowells ! co ! uk>
Date:       2007-09-03 12:33:09
Message-ID: 46DBFF05.2040502 () chrishowells ! co ! uk
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Hi John,

John Drescher wrote:
>> I believe the 120MB/s is the raw speed, 240MB/s is the compressed speed.
>>
> I tried to check on that but I did not find the direct answer. But I
> did find an article by IBM that stated that LTO4 did 120MB/s while
> LTO3 did 80MB/s. So I went to my tape vendor's web site and it stated
> that the 80MB/s for LTO3 was compressed with 40MB/s native so I came
> to the conclusion that the 120MB/s number was the compressed number...

Ah, you may well be right, I was in a rush and was using such reliable 
sources as Wikipedia ;)

I'll try and get a more definitive answer.

> You are correct. That is why I test with actual data from a raw partition.
> 
> Is this a SCSI tape drive? You might want to check on the speed it is
> communicating at (possibly stuck in LVD 80MB/s mode)...

It's actually SAS, so I don't believe that can be the problem.

Anyway, FWIW, I temporarily hooked the drive (with the same LSI SAS 
controller) up to a dual 3GHz Core 2 Duo. Got 91MB/s rather than 80MB/s 
writing zeros to the disk with dd, so the old Opteron does seem to be a 
tad lethargic.

Anyway, I've got multiplexing working, so I'm going to try backing up 
three clients tomorrow and see what kind of performance I get. I expect 
it will suck but we'll see :)

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