HP LTO tapes reports inconsistent number of blocks

[SubbuAkula]

Hi There,

$ mt -f /dev/rmt0 status

rmt0 Available 00-08-00 SAS 1/2-inch Cartridge Tape Drive

attribute     value            description                          user_settable

block_size    0                BLOCK size (0=variable length)       True

compress      yes              Use data COMPRESSION                 True

density_set_1 88               DENSITY setting #1                   True

density_set_2 70               DENSITY setting #2                   True

extfm         yes              Use EXTENDED file marks              True

mode          yes              Use DEVICE BUFFERS during writes     True

ret           no               RETENSION on tape change or reset    True

ret_error     no               RETURN error on tape change or reset True

size_in_mb    1500000          Size in Megabytes                    False

ww_id         50050763120ba5f7 World Wide Identifier                False

We are using a tape drive with block_size = 0 which means it takes block size from the issued cpio command.

We are using HP LTO -4 Ultrium RW - C7974A - 1.6TB tape.

EVerdyday it is writing/reading  with different number of blocks.

Below commands are used.

cpio -ocvB -- for writing

cpio -ictvB - for reading/verifying.

Please advise why there is inconsistency in the block numbers.

Thanks 

Subbu