Lun Masking And Mapping - HP 12000 Design Manual

Windows: Disable MS SCCM (System Center Config Mgr).
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HPUX: Ensure the EMS is not polling tape drives by either disabling it or by copying the
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archived dm_stape.cfg file to the /var/stm/config/tools/monitor folder, and
the polling interval can be set to 0 to disable polling.
HPUX: prevent utilities like mt from rewinding a tape that is in use by the backup
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application by turning on the HPUX kernel tunable parameter st_san_safe (which
disables tape device special files that are rewind-on-close)

LUN Masking and Mapping

By default, all hosts on the SAN can access all the virtual devices (libraries and tape drives) of the
VLS and this mode is used to easily share virtual drives across multiple media servers. (Enterprise
backup applications support the ability to share tape drives across multiple servers).
The backup applications take care of drive locking to ensure only one media server is using
one shared drive at a time.
VLS software manages the LUNs assigned to the VLS shared virtual devices by default. The
VLS changes device LUN assignments as needed to make sure that each Fibre Channel host
port has a LUN0, that there are no duplicate LUNs, and that there are no gaps in the LUN
numbering on a Fibre Channel host port (these are operating system requirements).
This is the easiest scheme for the backup administrator because they can simply configure all
their backup jobs across their media servers to use the shared library with shared drives and
the backup application takes care of deciding which drive is used for which backup job and
automatically scheduling all the jobs onto the available drives.
One disadvantage of this scheme is that if any one media server goes wrong (for example,
mixes up its tape drives paths), then it can interfere with the backups running from the other
media servers to the shared drives and can be very difficult to diagnose when there are many
media servers.
The VLS has an option to enable LUN masking in the device which is used to assign dedicated
virtual libraries/drives on a VLS. LUN masking lets you restrict which hosts you want to be visible
to particular virtual devices so that if a media server has any problem it only affects the tape drives
dedicated to that media server; it will not affect any backups on other media servers. Because LUN
masking prevents a host from seeing selected virtual devices on the Fibre Channel host ports, a
LUN-masked host will not see the virtual devices to which it does not have access and to which it
cannot write. This requires the administrator to manually allocate specific virtual drives in the virtual
library to specific media servers to meet their performance requirements.
40 Backup Solution Design Considerations