Datasheet

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3 IBM i using open storage configurations
3.1 Storage Area Networks 101
There are some basic SAN concepts that need to be understood by a person coming from an
integrated disks background:
 The disk drives installed in a SAN are not directly seen by IBM i. They are typically
grouped into RAID sets of drives called arrays, extent pools or storage pools. RAID 0, 1,
5, 6 and 10 are generally supported. The disks are RAIDed in the SAN and should not*
be protected on IBM i.
o * Note, the DS8000 has an option to present unprotected LUNs directly to IBM i,
where they would be protected by IBM i.
o Most SANs support different types of disk drives (ie fibre channel versus SATA)
and different disk drive speeds. Typical IBM i workloads work best with faster FC
or SAS drives versus SATA drives.
 After the RAID array is created, the SAN interface is used to create logical drives from
the space within the array.
o The user sets the size of the logical drives from a range of a few GBs to almost 2
TBs each. IBM i can handle drives anywhere in this range, except for restrictions
on the load source drive (35 GB minimum, 1.9 TB maximum). There is no need
to match the size of the supported integrated (internal) disk drives.
o IBM i performs best with logical drives that are the same size.
o IBM i has always been architected to perform best with more disk arms. This
does not change with SAN disks. You need to create a good number of logical
drives, not one large drive. Refer to the Storage planningPerformance section
for more details.
 The next step is to map or assign the logical drives to a host server. This server can be
VIOS or a direct connection to IBM i (depending upon the SAN being used. Refer to the
next two sections for details).
o Hosts are known by the Fibre Channel World Wide Port Name (WWPN) or the
SAS MAC address of the port on the adapter that the host server owns.
o A separate step, called SAN zoning, has to take place to configure the SAN
switches to connect the host adapter ports to the SAN’s host ports.
o As the logical drives are mapped to the host they are assigned a logical unit
number or LUN. A LUN is a unique number within an array. Many people refer
the logical drive as a LUN.
 On the VIOS host the mapped logical drives are seen as hdisks and then assigned to an
IBM i partition. It is recommended to assign whole hdisks to IBM i. VIOS supports logical
volumes where you can subset an hdisk into multiple volumes to assign to a partition.
This is not recommended for IBM i partitions.
 On an IBM i, the VIOS assigned drives or the direct attached mapped logical drives are
seen as DDxxx drives. The drives can be shown as “unprotected” but the SAN is
providing the protection. The drives can be added to any auxiliary storage pool (ASP)
that you choose.
3.2 IBM i open storage methods
There are three general methods by which IBM i connects to open storage:
 Directly through the SAN fabric without VIOS.
 As a client of VIOS, with VIOS connecting to a storage subsystem through the SAN fabric.
In this case VIOS sees the LUNs and then maps them as virtual SCSI (VSCSI) LUNS to
the IBM i client partition.