CHUNK    = 128*512
LV_START = 5120000*512
BSIZE    = 4096

found_byte = 47323856896
block_num  = (found_byte - LV_START) // BSIZE

print(f'Found at md0 byte: {found_byte}')
print(f'LV_START:          {LV_START}')
print(f'Offset from LV:    {found_byte - LV_START}')
print(f'Block number:      {block_num}')

virt      = block_num * BSIZE
group     = virt // (5*CHUNK)
in_group  = virt % (5*CHUNK)
chunk_idx = in_group // CHUNK
intra     = in_group % CHUNK

print(f'chunk_group={group} chunk_idx={chunk_idx} intra={intra}')
print()

# The block was found at chunk_idx=4 but IS readable
# This means our assumption that chunk_idx=4 = unreadable is WRONG
# The data IS there, we just need to read it

# Our current translation SKIPS chunk_idx=4
# But the data exists at: LV_START + group*5*CHUNK + 4*CHUNK + intra
# We've been computing: LV_START + group*4*CHUNK + chunk_idx*CHUNK + intra
# For chunk_idx < 4 these are equivalent
# For chunk_idx = 4 we skip it entirely

# So the fix is: for chunk_idx=4, read from the 5th physical chunk
# phys = LV_START + group*5*CHUNK + 4*CHUNK + intra
phys_5chunk = LV_START + group*5*CHUNK + 4*CHUNK + intra
print(f'Physical via 5-chunk formula: {phys_5chunk}')
print(f'Found at:                     {found_byte}')
print(f'Match: {phys_5chunk == found_byte}')