Half LTO 4 tape writing speed by increasing blocking factor from 1024 to 2048

Test description: Transfer 685 2K frames (11MB per file, 8.1 GB total)
to and from LTO 4 tape.

TAR Blocking Factor	Write LTO4	Read LTO4
1024	2m34s	1m16s
2048	1m24s	1m16s
4096	1m19s	1m34s

The organization writing the LTO4 tape can nearly halve write time
by using blocking factor of 2048 rather than 1024 as is commonly used.
Recommend we use blocking factor of 2048 on LTO 4 tapes.