Paul Furness wrote:
What does "block size" mean on a tape (DLT and LTO). Is it the same as old disks, where each file fills up at least one block, even if it's much smaller than a block? If I make this smaller, will more small files fit on the tape?
Block size refers to how much data is written to the tape in one chunk. This can have an effect on how much data you can write to the tape..
For each 'block' you write to the tape there is a pre-block gap , block header and then the actual data (possibly followed by a block trailer with CRC/checksum.
If you write your data in too-small chunks, then you can often end up wasting more space on the pre-gap and header than you do on the actual data.
If you write your data in too-large chunks, the tape may have to physically pause and wait for the data transfer to complete before writing the data when this happens you 'lose streaming', and the tape has to stop, backup and get back up to speed to write the next block This slows down the backup and adds wear & tear to the drive (and sometimes also wastes more space on the tape)
How do I get the tape drive to definitely use it's internal compression hardware? I don't think it's working and I need it to be. How can I check this from linux? Some of the auto-changers have displays on the front that specify whether compression is being used, but others don't.
man st for more info on the SCSI tape drivers.
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