Computer Drive User Manual

Chapter 10. FlashCopy performance 113
Table 10-1 FlashCopy source and target volume location
10.1.2 LSS/LCU versus rank considerations
In the DS6000 it is much more meaningful to discuss volume location in terms of ranks and
not in terms of logical subsystem (LSS) or logical control unit (LCU). On the ESS 800 and
earlier IBM disk subsystems, the physical locations of the volumes were described in terms of
the logical subsystem LSS/LCU. If there existed more than a single rank in the LSS/LCU,
then each of the ranks would have a range of volumes from that specific LSS/LCU.
The LSSs/LCUs in a DS6000 disk subsystem are logical constructs that are no longer tied to
predetermined ranks. Within the DS6000 the LSS/LCU can be configured to span one or
more ranks but is not limited to specific ranks. There can be individual ranks that contain
volumes from more than a single LSS/LCU, which was not possible before the introduction of
the DS6000.
10.1.3 Rank geometry
Finally, you can achieve a small performance improvement by using identical rank
geometries for both the source and target volumes. In other words, if the source volumes are
located on a rank with a 7+p/RAID-5 configuration, then the target volumes should also be
located on a rank configured as 7+p/RAID-5.
10.1.4 Incremental FlashCopy
This chapter focuses on FlashCopy performance best practices, but there are many other
business requirements that must be weighed when using FlashCopy. The designer should
carefully consider all aspects for the implementation of each specific solution and should
definitely evaluate the use of
incremental FlashCopy for all FlashCopy applications.
Tip: If the FlashCopy target volume is on the same rank as the FlashCopy source volume,
you run the risk of a rank failure causing the loss of both the source and the target volume.
Server Device Adapter Rank
FlashCopy establish
performance
Same server Don’t care Different ranks
Background copy
performance
Same server Different device adapter Different ranks
FlashCopy impact to
applications
Same server Don’t care Different ranks
Tip: To find the relative location of your volumes, you can use the following procedure:
1. Use the lsfbvol command to find out which Extent Pool contains the relevant volumes.
2. Use the lsrank command to display both the device adapter and the rank for each
Extent Pool.
3. To determine which server contains your volumes, look at the Extent Pool name. Even
numbered Extent Pools are always from Server 0, while odd numbered Extent Pools
are always from Server1.