- write in o_dsync instead of o_direct for smaller
objects to avoid unaligned double Write() situations
that may arise for smaller objects < 128KiB
- avoid fallocate() as its not useful since we do not
use Append() semantics anymore, fallocate is not useful
for streaming I/O we can save on a syscall
- createFile() doesn't need to validate `bucket` name
with a Lstat() call since createFile() is only used
to write at `minioTmpBucket`
- use io.Copy() when writing unAligned writes to allow
usage of ReadFrom() from *os.File providing zero
buffer writes().
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