HP StorageWorks 12000, User Manual

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VLS firmware version 2.x: By default, the VLS allows all hosts connected to the VLS through the SAN
to access all virtual devices configured on the VLS. Also, the VLS firmware manages the LUN mapping
so that the virtual device LUN assignments always meet operating system requirements and restrictions.
See “
Default LUN Numbering ” on page 121 and
“ Operating System LUN Requirements and Restrictions ” on page 121. Optionally, you can restrict host
access to individual virtual devices using the LUN masking feature then, for each LUN masked host,
to use the LUN mapping feature to manually assign LUN numbers to any virtual devices you want the
host to be able to access. See “
LUN Masking (v3.x) ” on page 122 and “ LUN Mapping (v3.x) ” on page
123 for reasons you may want to use these features.
Port mapping is required and allows you to assign each virtual device to one of the Fibre Channel
host ports or a pair of Fibre Channel host ports (if your backup solution supports this).
Default LUN Numbering
The VLS automatically assigns a logical unit number (LUN) to each virtual library and tape drive
created on the VLS in the order in which they are created by you, starting with LUN0 and increasing
incrementally by one as each new virtual library or tape drive is created on an Fibre Channel host
port (LUN1, LUN2, and so on). The first virtual device port mapped to any of the Fibre Channel host
ports is assigned the LUN number LUN0. The second virtual device port mapped to an Fibre Channel
host port is assigned the LUN number LUN1, and so on.
The default LUN numbers are changed by the VLS firmware when the VLS device emulations are
restarted if:
• A virtual device has been deleted since the last restart, creating a gap in the LUN numbering, or
• A virtual tape drive has been added to a library since the last restart and the default LUN number
it was assigned is not consecutive with the other virtual tape drives in the same library.
Restarting VLS device emulations changes the default LUN numbers as necessary to remove the gap
or to make the virtual tape drive LUN numbers consecutive in each library. This is done so that the
virtual device LUN numbering meets the operating system LUN requirements.
NOTE:
When a LUN has been unconfigured or otherwise deleted, it may still show up in the VLS user interface.
Use the VLS discovery utility to refresh the list of LUNs that are present.
Operating System LUN Requirements and Restrictions
Most operating systems require that each VLS Fibre Channel host port connected to the SAN has a
virtual device with the LUN number LUN0 and no gaps in the LUN numbering (LUN0, LUN1, LUN2,
and so on). If the operating system does not see a LUN0 on a VLS Fibre Channel host port when it is
scanning for new hardware on the SAN, it will stop looking for LUNs on that port and erroneously
report that there are no LUNs (virtual devices) on that port. If the operating system sees a LUN0, LUN1,
and LUN2 but not a LUN3 on the port, it will stop looking for LUNs on that port when the gap in the
LUN numbering is encountered. Even though there may be more LUNs, such as LUN4, the operating
system will erroneously report that there are only three LUNs on the port.
In addition, operating systems are configured to only look for a maximum number of LUNs per device
and no more. Once the maximum number of LUNs is detected, the operating system stops looking.
In the case of the VLS, the operating system considers each Fibre Channel host port to be one device
with its own set of LUNs. So, if the maximum number of LUNs an operating system is configured to
see is eight, the operating system will only see LUN0 through LUN7 and will not see LUN8, LUN9,
and up on each Fibre Channel host port.
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