On Wed, Jan 08, 2014 at 11:37:44AM -0500, Brian Cuttler wrote: ... > > The LTO is advertised as having block level decision making on > compression so that it doesn't expand the data, wonder if that > is not quite true.
My experience is limited to LTO-1, but I found amtapetype gave 'exactly' the same number of blocks capacity for compression on and off. > > Also - Isn't there another level of tape header that needs to be > cleared? Isn't re-writing the tape with compression off a little > bit of a trick? If you don't clear that other level of header, then > the compression is determined by the header info and not by the > device type selected when you write the tape? > Personal opinion; That whole "hidden header" is bogus, perpetuated by our friend Gene. It appears to be the situation if you turn off compression and try to use a previously compressed tape with amanda. However, remember what amanda always does before writing any tape (with the possible exception of amtapetype). It first reads the beginning of the tape for possible (and correct) amanda header. Reading a tape automatically sets the compression to whatever the tape previously used. So if the data currently on the tape is HW-compressed, the drive switches to HW-compress mode. > > [finsen]: /devices > /usr/local/sbin/tapeinfo -f /dev/rmt/3n > Product Type: Tape Drive > Vendor ID: 'HP ' > Product ID: 'Ultrium 4-SCSI ' > Revision: 'H5AW' > Attached Changer API: No > SerialNumber: 'HU1102EE9V' > MinBlock: 1 > MaxBlock: 16777215 > Ready: yes > BufferedMode: yes > Medium Type: Not Loaded > Density Code: 0x46 > BlockSize: 0 > DataCompEnabled: yes > DataCompCapable: yes > DataDeCompEnabled: yes > CompType: 0x1 > DeCompType: 0x1 > BOP: yes > Block Position: 0 > Partition 0 Remaining Kbytes: 800226 > Partition 0 Size in Kbytes: 800226 > ActivePartition: 0 > EarlyWarningSize: 0 > NumPartitions: 0 > MaxPartitions: 0 -- Jon H. LaBadie j...@jgcomp.com 11226 South Shore Rd. (703) 787-0688 (H) Reston, VA 20190 (609) 477-8330 (C)
