Hitachi Dynamic Link Manager Software Users Guide for AIX (6.6) (T5208-96010, April 2011)

2. HDLM Functions

then HDLM automatically places the recovered path online while a non-owner path is

in use, the path will be automatically switched over from the non-owner path to the

owner path that just recovered from the error.

When the Lightning 9900V series, Hitachi USP, Universal Storage Platform V/VM,

Virtual Storage Platform, Hitachi AMS2000 series, or Hitachi SMS is being used, all

the paths are owner paths. Therefore, if an owner path recovers from an error and

HDLM automatically places the recovered path online, the path to use is not switched.

When intermittent errors

occur on paths and you are using the automatic failback

function, the path status might frequently alternate between the online and offline

statuses. In such a case, because the performance of I/Os will most likely decrease, if

there are particular paths in which intermittent errors might be occurring, we

recommend that you set up intermittent error monitoring so you can detect these paths,

and then remove them from those subject to automatic failbacks.

You can specify the automatic failback function or intermittent error by the

dlnkmgr

command's

set operation. For details on the set operation, see 6.6 set (Sets Up the

Operating Environment).

An intermittent error means an error that occurs irregularly because of some

reason such as a loose cable connection.

2.7.2 Manual path switching

You can switch the status of a path by manually placing the path online or offline.

Manually switching a path is useful, for example, when system maintenance needs to

be done.

You can manually place a path online or offline by doing the following:

• Execute the

dlnkmgr command's online or offline operation.

For details on the

online operation, see 6.5 online (Places Paths Online). For

details on the

offline operation, see 6.4 offline (Places Paths Offline).

However, if there is only one online path for a particular LU, that path cannot be

manually switched offline. Also, a path with an error that has not been recovered from

yet cannot be switched online.

HDLM uses the same algorithms to select the path that will be used next, regardless of

whether automatic or manual path switching is used.

When using the Thunder 9500V series, or Hitachi AMS/WMS series, HDLM selects

the switching destination path from owner paths and then from non-owner paths.

When the Lightning 9900V series, Hitachi USP, Universal Storage Platform V/VM,

Virtual Storage Platform, Hitachi AMS2000 series, or Hitachi SMS is being used, all

paths that access the same LU are candidates for the switching destination path. All