Mysql alter table question
You need to ALTER a column from TEXT to MEDIUMTEXT?

Such an ALTER will copy the table over, making the change as it goes.  At the end, rebuild the indexes and will RENAME the table back into place.  The table will be blocked from (at least) writes for the duration, which could be hours.

For a less invasive approach, see pt-online-schema-change.  It will add a Trigger to the table so that writes are tracked while it copies the table over.  It ends with a brief finishing lock to flip the table into place.

Either approach will take about 5.7GB of spare disk space.  Caveat:  If you have innodb_file_per_table = OFF, the spare disk space will not be freed when finished.  I recommend ON when creating 'big' InnoDB tables.