# Test Case: FLAT_PLAIN Large File

**Test ID**: TC030-flat-plain-large

## Objective

Verify a greater-than-10-MiB contiguous `FLAT_PLAIN` file across thousands of
filesystem blocks.

## Fixture

Use `images/flat.erofs` and `source/flat/large.bin`. Evidence asserts layout 0
and size 10485791.

## Procedure

```sh
stat -f 'size=%z blocks=%b' "$mnt/large.bin"
dd if="$mnt/large.bin" of=/tmp/tc030-full bs=1m
cmp /tmp/repo22-g1/source/flat/large.bin /tmp/tc030-full
sha256 /tmp/repo22-g1/source/flat/large.bin /tmp/tc030-full
./read_probe pread "$mnt/large.bin" 5242880 1048576 /tmp/tc030-seek
dd if=/tmp/repo22-g1/source/flat/large.bin of=/tmp/tc030-source-seek \
  bs=1m skip=5 count=1
cmp /tmp/tc030-source-seek /tmp/tc030-seek
```

Remove all outputs, unmount, and detach.

## Expected Results

- Reported size is exact; full and seeked data match the source.
- No mapping error, panic, or cleanup failure occurs.
