[Stgt-devel] Dealing with filemarks in SSC ...

[Mark Harvey]

Both NetBackup and NetWorker use the following filemark handling.

[data][filemark1][data][filemark1][data][filemark1][filemark2]

Using the 'bsd' close (vs AT&T close), the tape head is positioned after
[filemark1] and before [filemark2]. A new 'write' command will overwrite
[filemark2].

Using this method, end of valid backup data is easily detected by two
consecutive filemarks on tape. If there is only one filemark, there is
more valid data to follow.

Note: filemark1 and filemark2 are just 'filemarks' - they are not
different types of filemarks. (Just in case this created any sort of
confusion).

Cheers
Mark

-----Original Message-----
From: stgt-devel-bounces at lists.berlios.de
[mailto:stgt-devel-bounces at lists.berlios.de] On Behalf Of Richard Sharpe
Sent: Wednesday, July 30, 2008 9:45 AM
To: stgt-devel
Subject: [Stgt-devel] Dealing with filemarks in SSC ...

I have been looking at this issue of filemarks in SSC, and it seems to
me that there are a couple of questions that need to be answered.

For example, if there are two file marks on a tape, or even three, and
you write records onto the tape and overwrite one of the file marks,
in some sense the drive should still be able to seek to the old second
filemark (now the first filemark) ... and reliably recover the third
file on the tape.

I don't know if any software depends on that behavior, though.
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