Veritas-bu

Re: [Veritas-bu] while vault duplication I/O oddity

2007-12-14 14:18:33
Subject: Re: [Veritas-bu] while vault duplication I/O oddity
From: Jon Bousselot <jon_bousselot AT sd.vrtx DOT com>
To: VERITAS-BU AT mailman.eng.auburn DOT edu
Date: Fri, 14 Dec 2007 10:54:53 -0800
I have seen this too.  If your source tape is multiplexed, NB will read all the contents of the tape and write only the image stream you requested to the destination.   If your source tape and images are heavily multiplexed, your write speeds will be significantly slower.  iostat shows throughput from the tape device, which is what the OS sees independent of what types of hardware compression you can get.  I have seen iostat show throughput spikes much higher than what the drive documentation claims, and this is due to an easily compressible data stream like an empty database file.
-Jon

Is the image multiplexed on the source tape?  If it is and you are created a de-muxed duplicate you will see this.


From: veritas-bu-bounces AT mailman.eng.auburn DOT edu on behalf of Chris_Millet
Sent: Fri 12/14/2007 12:22 PM
To: VERITAS-BU AT mailman.eng.auburn DOT edu
Subject: [Veritas-bu] while vault duplication I/O oddity


Ok, I'm watching iostat while vault is doing a duplication job.  For some reason, the read from the source tape is twice as fast as the write. 

For instance, I will see 60MB/sec of reads from source tape and maybe 30MB/sec of writes. 

What would cause this?  This is a new issue on this environment.  I typically see vaults match speed on reads/writes.

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