644 Implementing the IBM Storwize V5000 Gen2 with IBM Spectrum Virtualize V8.1
11.1.3 External storage configuration planning
Logical units that are created on the external storage system must provide redundancy
through various RAID levels, preventing a single physical disk failure from causing a managed
disk (MDisk), storage pool, or associated host volume from getting offline. To minimize the
risk of data loss, virtualize storage systems only where logical unit numbers (LUNs) are
configured by using a RAID level other than RAID 0 (RAID 1, RAID 10, RAID 0+1, RAID 5,
RAID 6, Distributed RAID 5, or Distributed RAID 6):
1. Verify that the storage controllers to be virtualized by the IBM Storwize V5030 meet the
configuration restrictions, which are listed on the IBM Support home page, at this website:
https://ibm.biz/BdjSJx
2. Ensure that the firmware or microcode levels of the storage controllers to be virtualized
are supported by the IBM Storwize V5030. See the IBM System Storage Interoperation
Center (SSIC) website for more details:
https://ibm.biz/BdjGMp
The IBM Storwize V5030 must have exclusive access to the LUNs from the external
storage system that are presented to it. LUNs cannot be shared between the IBM Storwize
V5030 and other storage virtualization platforms or between an IBM Storwize V5030 and
hosts. However, different LUNs can be mapped from the same external storage system to
an IBM Storwize V5030 and other hosts in the SAN through different storage ports.
3. Ensure that the external storage subsystem LUN masking is configured to map all LUNs to
all of the WWPNs in the IBM Storwize V5030 storage system. Ensure that you check the
IBM Storwize V5030 IBM Knowledge Center and review the “Configuring and servicing
external storage system” topic before you prepare the external storage systems for
discovery from the IBM Storwize V5030 system. This Knowledge Center topic is at this
website:
https://ibm.biz/BdjGMJ
11.1.4 Guidelines for virtualizing external storage
When external storage is virtualized by using the IBM Storwize V5030, the following
guidelines must be followed:
Avoid splitting arrays into multiple LUNs at the external storage system level. When
possible, create a single LUN per array for mapping to the IBM Storwize V5030.
Use 6 - 8 disks per RAID group when you create the external LUNs, more than that and it
may result in a longer rebuild time in case of a single disk failure, affecting the
performance of the LUN and exposing it to complete failure if a second disk fails during the
rebuild. Additionally, the smaller the number of disks, the more likely it is that write
operations span an entire stripe (stripe size, which is multiplied by the number of
members, minus one). In this case, write performance is improved.
Except for Easy Tier, do not mix MDisks that vary in performance or reliability in the same
storage pool. Put only MDisks of the same size and performance into the same storage
pool. Likewise, group MDisks from different arrays into different pools. For more
information about Easy Tier, see Chapter 9, “Advanced features for storage efficiency” on
page 437.
Do not leave volumes in image mode. Use image mode only to import or export existing
data into or out of the IBM Storwize V5030. Migrate data from image mode volumes and
associated MDisks to other storage pools to benefit from storage virtualization and the
enhanced benefits of the Storwize V5030, such as Easy Tier.
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