IBM TS3500 Manual page 99

hour), the overall reduction in mount performance compared to a TS3500 Tape Library
without HD frames can range from no impact to a worst-case 50% reduction in mounts per
hour (for a 99% full library in which all expansion frames are HD frames). This reduction in
mount performance is determined by the distribution of tiers that cartridges are mounted
from and the need to destage least-recently-used (LRU) cartridges from the cartridge cache.
The library configuration and cartridge usage influences the reduction in mount performance
in the following ways:
•
Each non-HD frame in the configuration increases the mounts from Tier 0
• Unlicensed capacity decreases the mounts from the highest tiers and decreases the
time required for shuffle operations (load balancing ensures the highest tiers are the
last ones utilized)
• Lower capacity utilization decreases the mounts from the highest tiers and decreases
the time required for shuffle operations (load balancing ensures the highest tiers are
the last ones utilized)
• A higher ratio of cartridges that are mounted more than once (cartridge cache hits)
increases the mounts from Tiers 0 and 1
• Cartridge eject operations prior to mount operations reduce the need to destage LRU
cartridges (this is because eject operations empty some Tier 0 slots)
Eject and insert performance can also be impacted for a TS3500 Tape Library that includes
HD frames. The impact to eject performance is determined by factors similar to mount
performance (distribution of tiers from which cartridges are ejected). The impact to insert
performance is different because inserts tend to go to HD frames since Tier 0 slots are
nominally kept full. This impact to insert performance is determined by the following
factors:
• A shorter time delay between eject and insert operations increases the inserts to
non-HD frames (this is because eject operations will empty some number of Tier 0
slots)
• A shorter distance between the I/O stations used for inserts and the HD frames
decreases the insert move time to those frames
For more information about HD frames, see
Parent topic: Library performance
High density technology.