This is Drupal 6 cache
table. Server version: 5.1.49-1ubuntu8.1 (Ubuntu)
According to Can't Repair Mysql Table
Shut down your DB and back it up. Repair operations are dangerous.
but according to http://www.techrepublic.com/article/checking-and-repairing-mysql-tables/5193721
The first—and most important—thing you can do before repairing a corrupted table is to back it up.
Next, shut down the MySQL server.
I've tried what techrepublic says... but I got this message from mysqlhotcopy:
DBD::mysql::db do failed: Table './dbname/cache' is marked as crashed and last (automatic?) repair failed at /usr/bin/mysqlhotcopy line 460.
and I got this message from mysqldump:
mysqldump: Couldn't execute 'show create table `cache`': Table './dbname/cache' is marked as crashed and last (automatic?) repair failed (144)