forum.lissyara.su

HAST can be compared to a RAID1 (mirror) where one of the components is local disk (on primary node) and second component is disk on remote machine (secondary node). Every write, delete or flush operation (BIO_WRITE, BIO_DELETE, BIO_FLUSH) is send to local disk and to remote disk over TCP connection (if secondary node is available). Every read operation (BIO_READ) is served from local disk, unless local disk isn't up-to-date or an I/O error occurs, then read operation is send to secondary node (if it is, of course, available).