Extremely slow MyISAM slave updates I have 2 slaves where one is working as expected, but the other slave is extremely slow when executing update statements. The insert and delete statements are fast. 

I used the command check table tbl_name to see if any MyISAM table was corrupt. Both the slaves are MyISAM only.

I am using (AWS ec2 instance) ext3 for the fast slave and xfs for the the other. Is that the reason why the updates are taking time?
You can compare both slaves performance using Percona utilities mentioned below:


pt-heartbeat measures replication lag on a MySQL server. You can use it to update a master or monitor a replica. If possible, MySQL connection options are read from your .my.cnf file.
pt-table-checksum performs an online replication consistency check by executing checksum queries on the master, which produces different results on replicas that are inconsistent with the master.