The server started with innodb_force_recovery=1?
One approach:
- find the minimum innodb_force_recovery setting that gets the server running, then ...
- mysqldump the whole shebang to a safe place, if you can ...
- run check table on every table to find corrupted tables, or ...
run mysqldump on half of the 24TB, keep cutting by half till you find the table(s) that are corrupt.
- edit corruption out of the dump(s), restore from what's left, and you'll have to regenerate what was lost to corruption.
Counter-intuitively, this works better before 5.6.16, so it may be necessary to clone the involved data folders to another drive, install 5.6.15 on another machine or drive, copy over all mysql data files, adjust my.cnf accordingly, then walk through the above.
More suggestions at ...
https://www.percona.com/blog/2016/01/19/dealing-with-corrupted-innodb-data/
https://stackoverflow.com/questions/15304708/recover-mysql-database-from-ibdata1
https://serverfault.com/questions/851342/mysql-crashed-and-not-starting-even-after-adding-innodb-force-recovery
And institute regular backups at intervals smaller than the maximum amount of data you can afford to take time to recreate.