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mt-st has an option:

fast-eod： space directly to eod (and lose file number)

I run the eod operation with/without this option, but is seems no significant difference. Does fast-eod make difference with LTO tape?

My test data:

  • HP lto6 tape drive
  • write 8GB*312 files (2.5TB), block size 512K, disable compression
  • eod without this option from BOT: 4.7s
  • eod with this option from BOT: 4s
petertc
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1 Answers1

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mt-st eod command ultimately sends SCSI SPACE command to the drive regardless of fast-eod option. According to LTO SCSI reference, there are two parameters for this operation: CODE and COUNT.

CODE specifies the type of termination point of the operation, as shown below. For example, if CODE=3h, then LTO drive moves the tape forward until reaching EOD.

  • 0h : Block
  • 1h : Filemarks
  • 3h : EOD

COUNT is the number of logical objects to be spaced. This parameter will be ignored if CODE=3h. Even with CODE=0h or 1h, the operation is terminated at the EOD position if the drive encounters EOD while processing the command.

According to Linux tape driver, here are the parameters to be used depending on fast-eod option:

  • Enabled : CODE=3h
  • Disabled : CODE=1h and COUNT=8,388,607 (0x7fffff)

Thus, tape drive stops at the EOD potions regardless of Enabled/Disabled. The biggest question is that CODE=3h is faster than CODE=1h and COUNT=8388607? Here is a direct quote from Bacula document.

I just expect, that for older tape drives Filemarks may be slower than End-of-data, but not so much as in Solaris slow mode.

Kevin Nakamoto
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