Make write_sectors() faster by using BufWriter
Make write_sectors() faster by using BufWriter

Use a 1 MiB buffer.

This will reduce the number of system calls we're making by ~2000x.

Signed-off-by: Andy Grover <b7d524d2f5cc5aebadb6b92b08d3ab26911cde33@redhat.com>

mulkieran/stratisd,trgill/stratisd,stratis-storage/stratisd,stratis-storage/stratisd,trgill/stratisd,mulkieran/stratisd,stratis-storage/stratisd