Hitachi Dynamic Link Manager Software Users Guide for Linux

Figure 4-1 Overview of the Period Required to Respond to an
Application's I/O Request
As shown in the preceding diagram, when an HDLM device has two paths
(SCSI devices), the maximum period of time required to respond to the
application's I/O request is n1 + n2 seconds; where n1 indicates the
timeout value specified for the path that uses SCSI device A, and n2
indicates the timeout value specified for the path that uses SCSI device B.
• When using HDLM in a cluster environment, a node in the cluster may fail
over before the path completes failover. To avoid this, when you set up
the failover timeout value for the node by using cluster software, make
sure that you specify a period longer than the response time that is
calculated as described in the preceding note.
• If a path error occurs while creating a file system, or formatting, or
executing fsck, the operation may not finish. In such a case, perform the
operation again after restoring the path error.
• The name of the HDLM device file will not be displayed on the Hardware
Browser of Red Hat Enterprise Linux.
• The Linux functionality that adds LABEL= to a SCSI device is not
supported in HDLM. Do not use this functionality. With HDLM, access can
constantly be made to the same LU if the name of the HDLM device file is
the same.
HDLM Operation
4-3
Hitachi Dynamic Link Manager (for Linux®) User Guide