On Mon, Jul 20, 2015 at 08:19:07AM +1200, [email protected] wrote: > Thanks Gene and Alan, > > Thank you for your recommendations. > > Seems that increasing of holding disk space does the trick, though I didn't > want to go that way. > > It's still not clear for me why "shoe shining" happens as the biggest > filesystem is located on the same server to which the tape drive is > connected to. > In my understanding a data stream should be passed to the taper using > loopback interface so it should have enough throughput for direct backup to > the tape. >
Tape drives must get the tape moving at their "writing speed" before they can actually write. So the drive when it stops positions itself before the next spot to write. This gives it tape space to speed up before reaching the next write position. If you have a fast tape it is very unlikely you can backup fast enough to actually feed the data fast enough for the drive to continuously stream. Thus it runs out of available data, stops, backs up, waits for data, speeds up, writes, runs out of data, stops, backs up, .... Thus it shoe-shines. The holding disk allows the backup to collect without tape involvement and when taped, hopefully stream at full speed to the drive. Jon -- Jon H. LaBadie [email protected] 11226 South Shore Rd. (703) 787-0688 (H) Reston, VA 20190 (703) 935-6720 (C)
