Disco saturado por mariadb no CentOS 7, bloqueia tudo

Nos últimos dias tenho tido problemas com um servidor web rodando CentOS 7. A cada 13-14 minutos alguma operação (que identifiquei com mariadb usando iostat) parece saturar completamente as operações de IO do disco, bloqueando todos os outros aplicativos. Após cerca de 3 minutos tudo volta ao normal.

Em /var/log/messages eu vejo:

Sep 14 09:35:42 MY-VM kernel: mptscsih: ioc0: attempting task abort! (sc=ffff9aefd1e76d80)
Sep 14 09:35:42 MY-VM kernel: sd 0:0:0:0: [sda] CDB: Write(10) 2a 00 2a 8b 1b 18 00 00 10 00
Sep 14 09:35:42 MY-VM kernel: mptscsih: ioc0: task abort: SUCCESS (rv=2002) (sc=ffff9aefd1e76d80)
Sep 14 09:35:42 MY-VM kernel: mptscsih: ioc0: attempting task abort! (sc=ffff9aefd1e741c0)
Sep 14 09:35:42 MY-VM kernel: sd 0:0:0:0: [sda] CDB: Write(10) 2a 00 0f 37 0a 58 00 00 08 00
Sep 14 09:35:42 MY-VM kernel: mptscsih: ioc0: task abort: SUCCESS (rv=2002) (sc=ffff9aefd1e741c0)
Sep 14 09:35:42 MY-VM kernel: mptscsih: ioc0: attempting task abort! (sc=ffff9aefd1e74700)
Sep 14 09:35:42 MY-VM kernel: sd 0:0:0:0: [sda] CDB: Write(10) 2a 00 0f 37 0a 38 00 00 10 00
Sep 14 09:35:42 MY-VM kernel: mptscsih: ioc0: task abort: SUCCESS (rv=2002) (sc=ffff9aefd1e74700)

Tenho monitorado as consultas, mas não consigo encontrar nada significativo.