IBM Storwize V7000 Unified Problem Determination Manual page 312

Monitoring file system compression
You can use the management GUI to monitor file and file system pool capacity
metrics in a single view by selecting Monitoring > Capacityand Files > File
Systems > Storage pools.
You can use two views to monitor the capacity usage on the system. Select
MonitoringCapacity to display a consolidated view of all information needed to
monitor capacity-related information on the system. In addition, you can create
alerts on capacity where you are notified when a specified capacity threshold has
been reached for file system or storage pool capacity. The Capacity View shows
system-wide compression savings and thin provisioning efficiency on storage pool
level.
The most important metric to monitor is the physical capacity that is used in the
storage pool. Make sure the physical allocation does not exceed the specified
threshold. The default threshold is set at 80%. To reduce the current utilization of
the used capacity, more physical capacity needs to be added to the storage pool or
data needs to be deleted from the file system. To view the current level of
utilization for block storage pools that are used for file system compression, select
Files > File Systems and ensure that the Storage pools filter is selected. The
management GUI displays all the file systems and their associated storage pools.
Select the file system and expand the file system pool to display the block storage
pool that is used for that file system. The Capacity column displays the current
used capacity for the file and the underlying block storage pools. To view specific
thresholds for individual volumes, select the NSDs filter to display the block
volumes that are used in the file system. To view specific thresholds for individual
volumes, right-click a volume and select Properties. In the upper right of the
Properties panel, an allocation bar is displayed with the current threshold indicated
by a red vertical bar.
Whenever a threshold is reached and an alert is issued, the system suggests actions
that correspond to the specific scenario. If action is not taken and the storage pool
reaches 100% utilization, volumes and their related network shared disks (NSDs)
can go offline, which causes the file system to go offline. To see an overview of
recovery scenarios, go to Chapter 8, "Troubleshooting compressed file systems," on
page 287.
Theoretically, the total virtual capacity for all volumes in a pool can exceed the
actual physical capacity that is available to the storage pool. For example, an
administrator creates a 10 TB file system from a storage pool that has 10 TB of
capacity. In this example, one volume is used and is allocated the full 10 TB of
capacity to store this data. On average, the data that is stored in this file system
has 60% compression savings. After the file system is full with 10 TB of data that
gets 60% compression savings, it has actually used only 4 TB of physical capacity
from the pool to store the compressed data. To use the remaining 6 TB of unused
capacity, virtual capacity can be added for the volumes in the pool.
However, in reality, you need contingency capacity on the storage pool that
remains unallocated and available to minimize impact to capacity utilization when
data changes affects compression rates. In most cases, data does not have the same
compression rate because it is constantly changing over the course of life cycle.
Incompressible data or data that does not compress well can be added to a file
system, which impacts compression rates. The system default for the contingency
threshold at 80% of the physical capacity which provides 20% contingency capacity
for the storage pool, which is adequate for most environment. For example, if an
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Storwize V7000 Unified: Problem Determination Guide 2073-720