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Header indexes and du -sk output

 
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Darren Lovatt
New Member

Header indexes and du -sk output

Hi all!

I understand that the index size reported on a tape header represents the 'intended' amount of data fbackup will attempt to backup - but why does this not match the output from a 'du -sk' ?

What's the best way to determine just how much data fbackup will attempt to backup, prior to starting the backup process?

Many thanks
Darren
4 REPLIES 4
harry d brown jr
Honored Contributor

Re: Header indexes and du -sk output

Darren, although you might have differences between "du" and fbackup, they shouldn't be "huge". Is the directory you are looking at have many hundreds of thousands of files? What kind of differences are you seeing?

live free or die
harry
Live Free or Die
Darren Lovatt
New Member

Re: Header indexes and du -sk output

Hi Harry

Thanks for your reply.

We have over 200 unix servers and each has a full backup each week. Recently, many of these have been asking for a second tape (we use 120m DDS2's). Typically, the index size is somewhere around the 8Gb mark, but 'du -sk' returns up to 2Gb less than that.

Many thanks
Darren
James R. Ferguson
Acclaimed Contributor
Solution

Re: Header indexes and du -sk output

Hi Darren:

The most likely cause would be inuse files that are recopied.

'fbackup' is designed to backup active filesystems. When a file is copied to tape, 'fbackup' makes note of its timestamp at the beginning of the transfer and compares it to the timestamp of the file *on disk* once it has been fully copied to tape. If the timestamps match, the tape copy for that file is "good". If the timestamps don't match the file on tape is marked as "bad" and another attempt is made to copy from disk to tape. This cycle of "note", "copy", "compare" is repeated 'maxretries' as specified by the 'config' file used with the 'fbackup' session (see 'man 1M fbackup'). The default number of retries is five.

Marking the file as "bad" on the tape allows 'frecover' to skip it as necessary. However, the penalty is that extra tape is used for every retry whether or not a good copy is ever achieved.

I personally like to run 'fbackup' with '-v'erbose logging redirected to a file from which I can extract warning messages like retries. Too, if any warning messages are generated during an 'fbackup' session, 'fbackup' will return a value of four (4).

Regards!

...JRF...
Darren Lovatt
New Member

Re: Header indexes and du -sk output

Hi James and thankyou for your assistance.

I can understand how such retries would affect the amount of data physically written to tape, but would they affect the index size as reported in the tape volume header before any data has actually been written?

It would be nice if I could just run the section of the fbackup program which estimates how much data is to be backed up.

Many thanks again
Darren