IBM DS8700, Введение и руководство по планированию

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When you enable auto-rebalance, every standard and ESE volume is placed under
Easy Tier management for auto-rebalancing procedures. Using auto-rebalance gives
you the advantage of these automatic functions:
v
Easy Tier operates within a tier, inside a managed storage pool.
v Easy Tier automatically detects performance skew and rebalances extents within
the same tier.
In any tier, placing highly active (hot) data on the same physical rank can cause
the hot rank or the associated device adapter (DA) to become a performance
bottleneck. Likewise, over time skews can appear within a single tier that cannot
be addressed by migrating data to a faster tier alone, and require some degree of
workload rebalancing within the same tier. Auto-rebalance addresses these issues
within a tier in both hybrid and homogenous pools. It also helps the system
respond in a more timely and appropriate manner to overloading, skews, and any
under-utilization that can occur from the addition or deletion of hardware,
migration of extents between tiers, changes in the underlying volume
configurations, and variations in the workload. Auto-rebalance adjusts the system
to continuously provide optimal performance by balancing the load on the ranks
and on DA pairs.
The latest version of Easy Tier provides support for auto-rebalancing within
homogenous pools. If you set the Easy Tier Automatic Mode Migration control to
Manage All Extent Pools, extent pools with a single-tier can perform intra-tier rank
rebalancing. If Easy Tier is turned off, then no volumes are managed. If Easy Tier
is on, it manages all the volumes it supports, standard or ESE.TSE volumes are not
supported with auto-rebalancing.
Notes:
v
Standard and ESE volumes are supported.
v In the previous version of Easy Tier, merging pools was restricted to
allow auxiliary volumes only in a single pool, and they were not
supported on SSD ranks of hybrid pools. However, in this enhanced
version of Easy Tier, these restrictions apply only to repository auxiliary
volumes.
v
If Easy Tier’s Automatic Mode Migration control is set to Manage All
Extent Pools, then single-tier extent pools are also managed to perform
intra-tier rank rebalancing.
Warm demotion
Warm demotion operation demotes warm (or mostly sequential-accessed) extents
in SSD to HDD, or from Enterprise SAS to NearLine SAS drives (DS8800) to
protect the drive performance on the system. Warm demotion was first available in
version 6, release 1, the second release of Easy Tier. In both this release and the
previous release, the ranks being demoted to are selected randomly. This function
is triggered when bandwidth thresholds are exceeded. This means that extents are
warm-demoted from one rank to another rank among tiers when extents have high
bandwidth but low IOPS.
It is helpful to understand that warm demotion is different from auto-rebalancing.
While both warm demotion and auto-rebalancing can be event-based, rebalancing
movement takes place within the same tier while warm demotion takes place
among more than one tier. Auto-rebalance can initiate when the rank configuration
changes. It also performs periodic checking for workload that is not balanced
across ranks. Warm demotion initiates when an overloaded rank is detected.
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Introduction and Planning Guide