Select Temporary Removal Thresholds from the
Actions menu to lower the removal threshold for a TS7700 Cluster in the grid.
Note: This page is disabled if the grid possesses a physical library but
the selected cluster does not. This page is not visible if the grid does not possess a physical
library.
For a TS7700 Cluster in a
grid, you can use this option to lower the threshold at which virtual volumes are removed from
cache. When the threshold is lowered, additional virtual volumes already copied to another cluster
are removed, creating additional cache space for host operations. This is necessary to ensure that
virtual volume copies can be made and validated prior to a Service mode event.
Virtual volumes may need to be removed before one or more clusters enter Service mode. When a
cluster in the grid enters Service mode, remaining clusters can lose their ability to make or
validate volume copies, preventing the removal of an adequate number of virtual volumes. This
scenario can quickly lead to the TS7700 Disk Only Cluster Cache or the
resident partition (partition 0) of a TS7700 Tape Attach Cluster to reach its
maximum capacity. The lower threshold creates additional free cache space, which allows the TS7700 to accept any host requests or
copies during the service outage without reaching its maximum cache capacity.
The Temporary Removal Threshold is used to temporarily establish a removal threshold that is
lower than the default, or permanent, removal threshold.
If the TS7700 attaches to a tape library, the
value of the threshold is determined by partition 0.
- (Permanent) Removal Thresholds
- The default, or permanent, Removal Threshold is used to prevent a cache overrun condition in a
TS7700 Cluster that is configured as part of a grid. By default it is a 4 TB value (3 TB fixed plus
1 TB) that, when taken with the amount of used cache, defines the upper size limit for a TS7700
Cache or for a TS7700 Tape Attach CP0. Above this threshold, virtual volumes begin to be removed
from a TS7700 Cache. Virtual volumes are removed from a TS7700 Cache in this order:
- Volumes in scratch categories
- Private volumes least recently used, using the enhanced removal policy definitions
Once removal begins, the TS7700 continues to remove virtual
volumes until the Stop Threshold is met. The Stop Threshold is a value that is the Removal Threshold
minus 500 GB.
- A particular virtual volume cannot be removed from a TS7700 Cache until
the TS7700 verifies
that a consistent copy exists on a peer cluster. If a peer cluster
is not available, or a volume copy has not yet completed, the virtual
volume is not a candidate for removal until the appropriate number
of copies can be verified later.
-
Note: The default removal threshold can be changed
from the command line, by using the following library request command:
LIBRARY REQUEST library-name,SETTING,CACHE,REMVTHR,{VALUE}
- Temporary Removal Thresholds
- The Temporary Removal Threshold lowers the default Removal Threshold to a value lower than the
Stop Threshold in anticipation of a Service mode event.
- The Temporary Removal Threshold value must be equal to or greater
than the expected amount of compressed host workload written, copied,
or both to the TS7700 during the service outage. The Temporary Removal
Threshold is 4 TB providing 5 TB (4 TB plus 1 TB) of free space exists,
but you can lower the threshold to any value between 2 TB and full
capacity minus 2 TB.
- All TS7700 Clusters in the
grid that remain available automatically lower their Removal Thresholds to the Temporary Removal
Threshold value defined for each. Each TS7700 Cluster may use a different
Temporary Removal Threshold. The default Temporary Removal Threshold value is 4 TB or an additional
1 TB more data than the default removal threshold of 3 TB. Each TS7700 Cluster will use its defined
value until any cluster in the grid enters Service mode or the temporary removal process is
canceled. The cluster that initiates the temporary removal process will not lower its own removal
threshold during this process.
Table 1. Details of the Temporary Removal Threshold modal window
| Element |
Description |
| Enable Temporary Thresholds |
Check this box and click OK to start the preremoval
process. Uncheck this box and click OK to abandon a current preremoval
process. |
| Initiate the removal process from: |
Select from this drop-down menu the cluster that will be put into Service
mode. The pre-removal process is started on this cluster. Note: This process does not initiate
Service Prep mode.
If the cluster selected from this drop-down menu is a TS7700 Cluster then the cluster is
disabled in the TS7700 List Subject to Auto Removal since
Temporary Removal Threshold would not be lowered on this
cluster. |
| TS7700 List Subject to Auto Removal |
This area of the modal window contains each TS7700 in the grid and a text field to
set the temporary removal threshold for that cluster. |
Table 2.
| Header |
Header |
| Capacity tube images |
Hover over a specific tube image in the TS7720
List area to highlight it and display the current threshold
setting for the associated cluster. Each image also displays the following
cache capacity information:
- Licensed Capacity
- The maximum licensed amount of available cache. This value is
shown at the top of the image.
- Total Used Cache
- The total amount of all used cache. This value is the sum of all
cache sizes defined by removal policies. In the image it is shown
as the compound value comprised of those removal policy values and
internal metadata.
- Size of cache defined by any removal policies
- The amount of cache defined by a given removal policy, including:
- Prefer Remove
- Prefer Keep
- Pinned
In the image, these values comprise the compound value Total
Used Cache.
- Refer to the cache capacity tube on the Cluster Summary panel
for additional information about the amount of cache defined by a
specific removal policy.
- (Permanent) Removal Threshold
- A light blue line that denotes a fixed, 4 TB value that, when
taken with the amount of used cache, defines the upper limit of a TS7720 Cluster size.
Above this threshold, virtual volumes begin to be removed from a TS7720 Cluster.
- Hover over this line to display the threshold value.
- Temporary Removal Threshold
- A dark blue line that denotes the level to which the removal threshold
is temporarily lowered in anticipation of a Service mode event. This
value must be lower than the Stop Threshold.
- Hover over this line to display the threshold value and an editable
lower threshold value field.
- Lower threshold
- An editable field displayed to the right of the Temporary
Removal Threshold.
- The Temporary Removal Threshold value must
be equal to or greater than the expected amount of compressed host
workload written, copied, or both to the TS7720 Cluster during
the service outage. By default, this value is 4 TB providing 5 TB
(4 TB plus 1 TB) of free space exists, but you can lower the threshold
to any value between 3 TB and full capacity minus 3 TB.
- Hover over the help icon next to this field to display a range
of possible threshold values. Enter a new value and click OK to
modify the lower threshold value.
Note: This field is unavailable if
the selected cluster is the only TS7720 Cluster (not
connected to a physical library) in the grid.
You can monitor
or cancel an in-progress threshold lowering option on the Tasks page.
A threshold lowering operation remains in progress until it is canceled
or the cluster scheduled for service enters Service mode or goes offline.
|