snmdla-tm
2 Iron

query tape media block size

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Networker 8.0 has the following new feature, according to the release notes:

   LTO device default block size increases to 256 KB

      In NetWorker 8.0 SP1 and later, the default block size for an

      LTO device increases from 128 KB to 256 KB. When NetWorker

      labels a new or used volume in an LTO device and the Device

      block size attribute of the device is the handler default, then

      the label operation uses a 256 KB block size. Increasing the

      default LTO block size results in Data Domain VTL deduplication

      ratios improving by up to 15%, and physical tape device write

      speed over higher-latency SAN links improving by an average 30%.

      Note: Volumes will not write at the new block size until the

      volume is labeled with NetWorker 8.0 SP1.

Now, after we wrote some LTO tapes with the new Networker, I would like to see what block size was used.

I did not find a NMC dialogue to query this tape attribute, nor does mminfo provide information about the actual block size written.

Thanks for any assistance,

Thomas

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nmc2
3 Silver

Re: query tape media block size

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Load the tape into drive and run the scanner command. Syntax here below,

scanner -v <device_name>

this command will read through the tape information, wait for  few seconds seconds after the scanner starts, it will report the block size and other information. Hit ctrl+c to stop scanner. You don't have to wait for entire tape scanner to complete.


Here is an example output,

# scanner -v /dev/nst0

8909:scanner: using '/dev/nst0' as the device name

9000:scanner: /dev/nst0: opened for reading

9003:scanner: /dev/nst0: rewinding

9067:scanner: Rewinding done

8968:scanner: Reading the label...

8969:scanner: Reading the label done

8936:scanner: scanning LTO Ultrium-5 tape E01004L4 on /dev/nst0

96367:scanner: volume id 4110497332 record size 262144 bytes

  created  3/12/15 12:16:12 expires  3/11/17 12:16:12

9003:scanner: /dev/nst0: rewinding

9067:scanner: Rewinding done

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ble1
6 Indium

Re: query tape media block size

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In device properties you have device block size setting.  What text says is not feature but just note that default 128KB was increased to 256KB - by default people used to set this in past manually to 256KB themselves for performance reasons.

You can check what you use by checking what block size is set in each device property.  If it says handler default, then it is default internal setting for that particular media (in past you could dump those with NSR_DEV_BLOCK_SIZE_MSG=YES variable).  You can also see impact of various block sizes when using tape_perf_test command.

snmdla-tm
2 Iron

Re: query tape media block size

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Hrvoje,

thanks. I already found this setting, and is set to "handler default".

Now the actual issue is about finding out afterwards, when a tape has been re-labeled, what block size was chosen by networker.

Thanks, Thomas

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bingo.1
4 Germanium

Re: query tape media block size

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The setup is one thing - but which block size was used when the tape was actually written?

This is especially important if you read (older) tapes from another data zone.

To verify that, simply run the 'scanner' command - it will report the block size found.

ble1
6 Indium

Re: query tape media block size

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I'm not sure if tape is re-labeled; it might use existing bs from header or the one in device properties.  Chances are that is more feasible that it reads current setting on device, but you can test it.  To see which bs you have, you can use scanner command.  Having it set to bigger one is not an issue; imagine setting for bs to be your mouth while actual bs is egg. Obviously, egg smaller than your mouth will pass through - other way around I'm afraid it won't.

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snmdla-tm
2 Iron

Re: query tape media block size

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bingo and Hrvoje are recommending the scanner command. 2 questions arise:

  • isn't there a way to query that information from Networks media metadata without physical access
  • if scanner is the only command, how can I check only a few blocks an exit then. When I fiddled around with scanner, it always would read in the whole tape

Greetings, Thomas

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nmc2
3 Silver

Re: query tape media block size

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Load the tape into drive and run the scanner command. Syntax here below,

scanner -v <device_name>

this command will read through the tape information, wait for  few seconds seconds after the scanner starts, it will report the block size and other information. Hit ctrl+c to stop scanner. You don't have to wait for entire tape scanner to complete.


Here is an example output,

# scanner -v /dev/nst0

8909:scanner: using '/dev/nst0' as the device name

9000:scanner: /dev/nst0: opened for reading

9003:scanner: /dev/nst0: rewinding

9067:scanner: Rewinding done

8968:scanner: Reading the label...

8969:scanner: Reading the label done

8936:scanner: scanning LTO Ultrium-5 tape E01004L4 on /dev/nst0

96367:scanner: volume id 4110497332 record size 262144 bytes

  created  3/12/15 12:16:12 expires  3/11/17 12:16:12

9003:scanner: /dev/nst0: rewinding

9067:scanner: Rewinding done

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ble1
6 Indium

Re: query tape media block size

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snmdla-tm wrote:

bingo and Hrvoje are recommending the scanner command. 2 questions arise:

  • isn't there a way to query that information from Networks media metadata without physical access
  • if scanner is the only command, how can I check only a few blocks an exit then. When I fiddled around with scanner, it always would read in the whole tape

Greetings, Thomas

a) Nope, this data is written within label (2x32KB block containing information about volume)

b) ctrl+c is your friend (and you can use -n switch too so that you do not scan any data)