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Space Borrowing for Snapshots and Replicas
Dell PS Series firmware v8.0
Dell Storage Engineering
June 2015
A Dell Best Practices Guide
Revisions
Date
Description
September 2012
Initial release
June 2015
Updates for Dell PS Series firmware v8.0, including Space Borrowing for Replication
Acknowledgements
Author: Michael Pacheco
THIS WHITE PAPER IS FOR INFORMATIONAL PURPOSES ONLY, AND MAY CONTAIN TYPOGRAPHICAL ERRORS AND TECHNICAL INACCURACIES.
THE CONTENT IS PROVIDED AS IS, WITHOUT EXPRESS OR IMPLIED WARRANTIES OF ANY KIND.
© 2015 Dell Inc. All rights reserved. Dell, the DELL logo, and the DELL badge are trademarks of Dell Inc. Other trademarks and trade names may be
used in this document to refer to either the entities claiming the marks and names or their products. Dell disclaims any proprietary interest in the
marks and names of others.
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Table of contents
Revisions ............................................................................................................................................................................................. 2
Acknowledgements .......................................................................................................................................................................... 2
Audience ............................................................................................................................................................................................. 4
Objective ............................................................................................................................................................................................ 4
Introduction ....................................................................................................................................................................................... 4
1
Space borrowing ........................................................................................................................................................................ 5
1.1
Snapshots ......................................................................................................................................................................... 6
1.1.1 Snapshot reserve ............................................................................................................................................................. 6
1.2
Asynchronous replication .............................................................................................................................................. 8
1.2.1 Replication Space ............................................................................................................................................................ 9
2
Best practices for space borrowing ...................................................................................................................................... 10
2.1
Planning space requirements ..................................................................................................................................... 10
2.2
Space borrowing prioritization ................................................................................................................................... 10
2.3
Space borrowing behavior with changes to storage pools................................................................................... 10
2.4
Space borrowing for replication................................................................................................................................. 10
3
Space borrowing with thin provisioned volumes and SCSI UNMAP .............................................................................. 12
4
Displaying borrowed space information ............................................................................................................................. 13
4.1.1 Local Space tab ............................................................................................................................................................. 15
4.1.2 Remote Delegated Space tab ..................................................................................................................................... 18
5
Space borrowing examples ...................................................................................................................................................20
5.1.1 Space borrowing with snapshots ...............................................................................................................................20
5.1.2 Space borrowing with snapshots and replication schedules ................................................................................ 21
5.1.3 Space borrowing with low delegated space on the secondary group (replication) ......................................... 23
5.1.4 Space borrowing with low total replica reserve (replication) ............................................................................... 26
A
3
Additional resources................................................................................................................................................................30
A.1
Technical support and customer service .................................................................................................................30
A.2
Dell online services .......................................................................................................................................................30
A.3
Dell PS Series storage solutions .................................................................................................................................30
A.4
Related documentation ...............................................................................................................................................30
Space Borrowing for Snapshots and Replicas | TR1084 | version 2
Audience
The information in this guide is intended for technology professionals interested in using Dell PS Series
storage to protect and recover data using PS Series snapshots and replicas.
Objective
This guide details the space borrowing features in Dell PS Series firmware v8.0 and later for snapshots and
replicas.
Introduction
Storage plays a critical role in business operations. With the ever-growing presence of new applications
and data, storage demands continue to grow. Dell PS Series provides support for block storage with PS
Series firmware, and Network Attached Storage (NAS) with FS Series firmware, delivering high
performance, high availability, scalability, and on-demand provisioning in a unified storage environment.
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1
Space borrowing
In a Dell PS Series group, snapshots and replicas are space-efficient, point-in-time copies of a volume that
can be used to protect data and are often used to recover data lost by human error and data corruption.
Snapshots and replicas require available disk space to operate successfully. This disk space is referred to as
snapshot reserve and replica reserve. To determine the optimal amount of reserve space for snapshots
and replicas, it is a best practice to use the default space values, monitor activity over time, analyze the
space usage, and make adjustments as necessary. These precautions will help you keep the desired
number of snapshots and replicas while using space efficiently.
Space usage is not always predictable, however, and sometimes it is difficult to determine the optimal
values to use for reserves. For example, if reserves are set too high, then space is wasted. If reserves are set
too low, then it is difficult to maintain the desired number of snapshots and replicas to keep. If, for
example, free reserve space is low in a pool for snapshots, or within delegated space for replicas, then
creating another snapshot or replica can potentially force older snapshots and replicas to be prematurely
deleted.
Dell PS Series firmware version 8.0 provides the ability for snapshots, local and remote replicas, and
deleted volumes in the Group Volume Recovery Bin to temporarily borrow space beyond the configured
reserves. This feature, called space borrowing, simplifies configuring reserve space, improves space
utilization, and enhances management of snapshots and replica reserves.
Note: Previous versions of Dell PS Series firmware (6.x and 7.x) provided space borrowing for snapshots
and local replication operations only.
Borrowed space is a subset of the storage pool’s total space and can allow older snapshots and replicas to
remain if space is available to borrow. Borrowed space is automatically reclaimed when necessary. Space
is potentially available for borrowing from the following areas:




Unused snapshot reserve
Unused local replication reserve on the primary and secondary groups
Unused delegated space
Free space in the storage pool where the snapshot or replica resides; space cannot be borrowed from
another pool.
Space cannot be borrowed from:
 Unused volume reserve: Unused Space that has been reserved for volumes.
 NAS storage container: NAS containers are used by Dell Storage FS Series nodes to create NAS shares.
Since these volumes do not contain PS Series snapshots or replicas, they are not available for space
borrowing.
 VVol (Virtual Volume) storage container: VVol Storage containers are used with VMware environments
and cannot be used to hold standard PS Series volumes, snapshots, replicas, or NAS containers.
Storage containers are not supported outside of the VMware Virtual Volumes context.
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For examples on using Space Borrowing with Snapshots and Replicas, please refer to: Space Borrowing
Examples.
1.1
Snapshots
In a PS Series group, Snapshots are space-efficient, point-in-time copies of a volume that can be used to
protect data and are often used to recover data lost by human error and data corruption. Multiple
snapshots of a volume can be retained for data protection and are accessible to other hosts.
When a Snapshot of a volume is created, it does not initially consume any space (as the snapshot shares all
data with the volume), but instead is a set of pointers to the data in the base volume. As data is modified
on the base volume, disk space is allocated from the snapshot reserve to store the modified data.
Meanwhile, the snapshot still points to the original data pages so that the volume looks exactly like it did at
the point in time when the snapshot was taken.
1.1.1
Snapshot reserve
In order to create snapshots of a volume, the administrator must allocate snapshot reserve to hold the
snapshot data. Snapshot reserve space is consumed from the local group and pool where the volume
resides and is a percentage of a volume to be used to store its snapshots.
Note: Because snapshot reserve is a percentage of the volume reserve, the amount of snapshot reserve
space fluctuates in direct proportion to a thin-provisioned volume reserve when data is dynamically
written and deleted (for example, when invoking SCSI UNMAP from Microsoft® Windows®, VMware®
ESXi™ or Red Hat® Linux — see section 3).
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1.1.1.1
Snapshot reserve settings
Depending on the number of snapshots and the amount of changes made to the base volume, snapshot
reserve can become entirely consumed. If this happens, the default action is to delete the oldest snapshot,
providing the necessary free space to create a new snapshot. However, there are various other
configurable defaults for snapshot space.
Default Snapshot reserve settings can be managed at the PS Series group level, and at the individual
volume level.
Note: Modifying default Snapshot space settings at the group level affects subsequently created volumes,
not existing volumes.
To modify the default Snapshot policy for the entire PS Series group:
1. In Group Manager, select the group in the left pane.
2. Click Group Configuration.
3. Click the Defaults tab.
Snapshot space reserve settings use group default values, unless you explicitly change them for an
individual volume.
Table 1
7
Snapshot reserve settings
Item
Description
Snapshot space reserve
Amount of snapshot storage space, based on a percentage of the
volume, reserved in the local storage pool. If the size of a volume
changes, the amount of snapshot reserve also changes.
Warn when in-use space
reaches this percentage
of snapshot reserve
Percentage of the snapshot reserve, when reached by in-use snapshot
reserve, results in an event message. The default is 90 percent of the
snapshot reserve.
Snapshot space recovery
policy



Set the volume (and snapshots) offline
Delete the oldest snapshots to free space for new snapshots
Borrow snapshot space as needed
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To modify the Snapshot policy for an individual volume:
4.
5.
6.
7.
In Group Manager, click the group in the left pane.
Expand Volumes, right-click the volume and select Modify snapshot policy.
Select a snapshot space recovery option and click OK.
To enable space borrowing for snapshots, check Borrow snapshot space as needed.
For additional information on snapshots, refer to the following documents.


1.2
Dell EqualLogic Group Manager Administrator’s Manual on eqlsupport.dell.com (login required)
EqualLogic Snapshots and Clones: Best Practices and Sizing Guidelines on Dell TechCenter
Asynchronous replication
Replicas are also space-efficient, point-in-time copies of a volume that can be used to protect and
recover data. However, while snapshots of a volume reside in the same pool and PS Series group as the
base volume, replicas of a volume reside in a pool of a secondary PS Series group. Volume replication
between two PS Series groups provides protection against data loss. If a volume is destroyed in a primary
PS Series group, you can fail over and recover the data from a replica in a Secondary PS Series group. This
is commonly used to provide business continuity in disaster recovery situations such as regional disasters
and testing scenarios.
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1.2.1
Replication Space
Volume replication between partners requires space on both the primary group (the volume location) and
the secondary group (the replica location). These space requirements are classified as follows:
Delegated space on the secondary group, is the amount of space dedicated to storing replicas from the
primary group. All replica reserves are confined to exist within this configured limit.
Local replication reserve on the primary group, is the amount of space reserved in the pool for replication
operations.
Current replica volume reserve (in MB/GB/TB) on the secondary group, is the reserved space for
replication on the volume.
Total replica reserve is the amount of space reserved for the replica set within the configured delegated
space on the secondary group. Total replica reserve is a percentage of the current replica volume reserve
that provides additional space for replicas. If the current replica reserve is 1 GB, and you specify 200% for
total replica reserve, the total replica reserve size is 2 GB. If the current replica volume reserve increases to
4 GB, then the total replica reserve size also increases to 8 GB. The total replica reserve for a volume can
potentially limit the number of replicas that are kept. To prevent older replicas from being deleted, space
can automatically be borrowed from other sources when the total replica reserve is consumed.
Figure 1
Examples of group space usage
For additional information on using Asynchronous Replication with Dell PS Series, refer to:


9
Dell EqualLogic Group Manager Administrator’s Manual on eqlsupport.dell.com (login required)
Using Dell PS Series Asynchronous Replication on Dell TechCenter
Space Borrowing for Snapshots and Replicas | TR1084 | version 2
2
Best practices for space borrowing
For a system to gain the optimum benefit of space borrowing, apply the following best practices when
planning and configuring snapshot and replication storage space.
2.1
Planning space requirements
Space borrowing is intended to help during peaks of activity when additional space is needed temporarily.
It does not take the place of carefully provisioning reserves. For additional information on planning space
requirements for snapshots and replicas, refer to the following documents:



2.2
Dell EqualLogic Group Manager Administrator’s Manual on eqlsupport.dell.com (login required)
EqualLogic Snapshots and Clones: Best Practices and Sizing Guidelines on Dell TechCenter
Using Dell PS Series Asynchronous Replication on Dell TechCenter
Space borrowing prioritization
When necessary, the system automatically deletes a snapshot or replica that is borrowing space. Objects
using borrowed space are at risk for being deleted if the borrowed space is required to support another
operation with a higher priority. This could occur if a new snapshot of Volume A borrows snapshot reserve
from Volume B and then Volume B needs that space for its own snapshots.
Another example is space borrowed from free space in the storage pool that becomes needed to support
the creation of a new volume or expansion of an existing volume. This scenario could cause existing
snapshots and replicas that are borrowing the free space to be deleted. However, in-progress or last
successful replicas are never deleted automatically by this process.
2.3
Space borrowing behavior with changes to storage pools
If a volume or replica set is moved to another pool, the associated snapshots and replicas are bound to the
space borrowing limitations of the new pool. Also, if the size of a storage pool decreases due to the
removal of a member, this lowers the pool capacity as well as impacts the space borrowing capabilities.
2.4
Space borrowing for replication
While it is possible to enable or disable space borrowing for snapshots, space borrowing for replication is
automatic and cannot be disabled.
Remote replicas can borrow beyond their total replica reserve, but the total amount of configured reserve
space must still fit within the delegated space. If there is insufficient delegated space on the secondary
group, the system requires manual administrative intervention to increase the amount of delegated space.
Also, if the replica reserve for a volume is configured with a very low value, such as the minimum 105%,
the system can potentially require manual administrative intervention to increase the reserve percentage
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so that an in-progress replica can continue. In-progress replicas are not eligible to borrow space. See
section 5.1.4 for details.
Note: To use space borrowing for replicas, all members in the secondary group must be running Dell PS
Series firmware version 8.0 or later. Space borrowing for snapshots requires Dell PS Series firmware v6.0
or later.
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3
Space borrowing with thin provisioned volumes and SCSI
UNMAP
Snapshot reserve is defined as a percentage of volume reserve. If the volume size changes, the snapshot
reserve also adjusts automatically. With thin provisioned volumes using SCSI UNMAP (with Microsoft
Windows, VMware ESXi, or Red Hat Linux) where the PS Series volume size shrinks as a result of data being
deleted on the volume from the operating system, snapshot reserve will also shrink. Without space
borrowing enabled, this can potentially lead to older snapshots being deleted, if the reserve space
becomes entirely consumed.
Note: As a best practice, disable support for UNMAP from the operating system on hosts that are using
Dell PS Series volumes configured for replication (both asynchronous and synchronous).
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4
Displaying borrowed space information
To view borrowed space information in the PS Series group:
1.
In Group Manager, click Borrowed Space in the left pane.
You can also view space-borrowing statistics through several CLI commands. For additional information,
refer to the Dell EqualLogic Group Manager CLI Reference Guide at eqlsupport.dell.com (login required).
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1
2
1. Local Space tab: Displays space borrowing information for the local PS Series group (section 4.1.1).
2. Remote Delegated Space tab: Displays space borrowing information for remote PS Series groups
that are replication partners (section 4.1.2).
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4.1.1
Local Space tab
The Local Space tab displays space borrowing information for the local PS Series Group.
A
3
B
3
Callout
15
C
D
E
F
F
Description
A
Borrowed space by storage pool: This section summarizes borrowed space for the
selected pool or all pools.
B
Storage pool and resource column:
 Free space is the amount of unused space still available in the selected storage pool.
 Reserves are reserved space that can be borrowed and include snapshot reserve, local
replication reserve, and delegated space. Reserves do not include volume reserve or
storage containers for NAS or VVols.
C
Total column: Indicates the amount of space being used for each storage pool and
resource including snapshot and replica reserves, and free space. This data does not
include volume reserves and storage containers for NAS or VVols.
D
Used as designated column: Displays the amount of data that is consuming space within its
own reserve
E
Borrowed column: The total space that is being borrowed
F
Unused column: Denotes the amount of available space on each storage pool and
resource
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G
3
H
3
Callout
16
I
3
J
K
3
Description
G
Object types in <selected pool> that can borrow space section: A summary of the space
usage of objects that can borrow space in the selected pool. Types of objects that can
borrow space are:
 Snapshots
 Replica sets (inbound replicas in delegated space)
 Local replicas (outbound)
 Deleted volumes (in the Volume recovery bin)
H
Total reserves column: The amount of total reserve space allocated for each type of object
I
Total size column: The amount of space being used for each type of object
J
Reserves used column: The amount of reserve space being used for each type of object
K
Space borrowed column: The amount of space being borrowed for each type of object
Space Borrowing for Snapshots and Replicas | TR1084 | version 2
L
3
M
3
Callout
17
N
Q
3
P
3
Description
L
Objects in <selected pool> that can borrow space section: A list of objects that can borrow
space in the selected pool, including:
 Snapshots
 Replica sets (inbound replicas in delegated space)
 Local replicas (outbound)
 Deleted volumes (in the Volume recovery bin)
M
Total reserves column: The amount of space reserved for each object
N
Total size column: The amount of space being used for each object
O
Reserves used column: The amount of reserved space being used for each object
P
Space borrowed column: The amount of space being borrowed for each object
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4.1.2
Remote Delegated Space tab
The Remote Delegated Space tab displays space borrowing information for secondary groups that are
replication partners and summarizes the primary group delegated space usage at each replication partner.
The data is automatically updated each time the group communicates using a replication operation (such
as enabling replication on a volume or creating, modifying, or deleting a replica) with a replication partner.
Remote actions on the secondary group (such as deleting a replica) do not automatically trigger the GUI
to be refreshed with new information. However, the GUI can be manually refreshed to request an update.
A
B
Callout
18
C
D
E
F
G
Description
A
Delegated space by replication partner: section: Displays information about the replication
partners for the group
B
Delegated space column: The amount of delegated space allocated on selected replication
partner
C
Total replica reserves column: The amount of space reserved for replicas on each partner
D
Total size of replicas column: The amount of space being used for replicas on each partner
E
Reserves used column: The amount of reserved space being used for replicas on each
partner
F
Space borrowed column: The amount of space being borrowed for replicas on each partner
G
Last updated column: The last time the secondary group communicated with the primary
group
Space Borrowing for Snapshots and Replicas | TR1084 | version 2
H
J
K
L
M
N
O
I
19
Callout
Description
H
Replica sets on <selected partner> section: Displays information, supplied by the selected
replication partner, about the local group replica sets that exist on the selected replication
partner
I
Volume column: The name of the replica set on the selected partner
J
Number of replicas column: The number of replicas in the replica set
K
Total reserves column: The amount of space reserved for replicas on the volume
L
Total size column: The amount of space being used for replicas on the volume
M
Reserves used column: The amount of reserved space being used for replicas on the
volume
N
Space borrowed column: The amount of space borrowed for replicas on the volume
O
Last updated column: The last time the primary group communicated with the secondary
group. Some remote actions on the secondary group (such as deleting a replica) do not
automatically trigger the GUI to be refreshed with new information. Click Refresh to update
the GUI manually if required.
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5
Space borrowing examples
5.1.1
Space borrowing with snapshots
In the following example, a 10 GB thick volume is configured with 100% (10 GB) of snapshot reserve.
As snapshot borrowing is enabled on the volume, it is possible for the snapshot space to exceed the
configured 10 GB snapshot reserve for the volume. In the example below, the full 10 GB of configured
snapshot reserve space is being used, two additional GB are borrowed from the storage pool. A total of 12
GB of snapshot space is used. If snapshot space borrowing was not enabled, it would not be possible for
the snapshot space to exceed the initially configured 10 GB limit.
Note: Because snapshot reserve is a percentage of the volume reserve, the amount of snapshot reserve
space fluctuates in direct proportion to a thin-provisioned volume reserve when data is dynamically
written and deleted (for example, when invoking SCSI UNMAP from Microsoft Windows, VMware ESXi or
Red Hat Linux — see section 3).
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5.1.2
Space borrowing with snapshots and replication schedules
Space borrowing is also useful as it relates to snapshot and replication schedules. Because older
snapshots and replicas can borrow space and remain available even if the remaining reserve space runs
low.
In this example, a volume is configured with 200% replica reserve. This means that 100% is dedicated to
the current replica volume reserve (10 GB), and the remaining 100% (10 GB) is reserved for additional
replicas in the total replica reserve, for a total of 20 GB.
The configured replication schedule allows a maximum of five replicas to exist. This could, perhaps, be a
business requirement to help ensure that daily replicas exist for the last five days.
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Below, you can see that there are four existing replicas for the volume with a total a size of 19.82 GB,
which is closely approaching the configured 20 GB of replica reserve.
With space borrowing, the replication operation for the fifth replica succeeds and maintains all five
required replicas by enabling the four existing replicas to borrow 10.62 GB. Without space borrowing, this
replica set would not be able to maintain five replicas and would instead delete the older, existing replicas
in order to stay within the configured 20 GB replica reserve.
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5.1.3
Space borrowing with low delegated space on the secondary group
(replication)
Remote replicas can borrow beyond their total replica reserve, but the total amount of configured
reserve space must still fit within the delegated space.
In this example, a new 100 GB thick volume on the primary group is configured for replication with the
default total replica reserve, 200%. This means that 100% is dedicated to the current replica volume
reserve, and the remaining 100% is reserved for additional replicas in the total replica reserve.
When replication is enabled on this volume, a 100 GB thin-provisioned replica volume is created on the
secondary group, even though the primary volume is thick. This is typical behavior when enabling volume
replication. As the 100 GB replica volume is thin-provisioned, 10% of the replica volume will be reserved by
default for thin provisioning. This yields a 10 GB current replica volume reserve (10% of 100 GB).
Total replica reserve is a percentage of current replica volume reserve. As the total replica reserve is 200%,
and the current replica volume reserve is 10 GB, 200% of 10 GB results in a 20 GB total replica reserve.
100% of the 10 GB (10 GB) are in use in the current replica volume reserve, and a remaining 100% of the 10
GB (10 GB) is available for additional replicas in the total replica reserve.
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The secondary group is configured with 95 GB of delegated space for the primary group.
40 GB of data are written to the volume.
An attempt to replicate the volume fails with a critical alert, “Volume replication failed because the replica
reserve could not increase automatically due to lack of free delegated space. Contact the replication
partner administrator and request an increase in delegated space.”
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Writing 40 GB of data to the volume and creating a replica changes the current replica volume reserve to
50 GB. (40 GB of data + 10 GB current replica volume reserve = 50 GB).
Total replica reserve is a percentage of current replica volume reserve. As the total replica reserve is 200%,
and the current replica volume reserve is now 50 GB, 200% of 50 GB results in 100 GB of total replica
reserve. 100% of the 50 GB (50 GB) are in use in the current replica volume reserve, and a remaining 100%
of the 50 GB (50 GB) is available for additional replicas in the total replica reserve.
Even though there is plenty of borrowable space on the secondary group, the replication failed because
the volume total replica reserve, 100 GB, exceeds the secondary group delegated space of 95 GB. Remote
replicas can borrow beyond the total replica reserve, but the total amount of configured reserve space
must fit within the delegated space. If there is insufficient delegated space on the secondary group, the
system will require manual administrative intervention to increase the amount of delegated space.
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5.1.4
Space borrowing with low total replica reserve (replication)
Even with plenty of delegated space and borrowable space, if there is insufficient replica reserve on the
secondary group, the system will require manual administrative intervention to increase the amount of
total replica reserve space to complete an active replication operation.
In this example, a new 100 GB thick volume on the primary group is configured for replication with the
minimum total replica reserve, 105%. This means that 100% is dedicated to the current replica volume
reserve, and 5% is reserved for additional replicas in the total replica reserve.
When replication is enabled on this volume, a 100 GB thin-provisioned replica volume will be created on
the secondary group, even though the primary volume is thick. This is typical behavior when enabling
volume replication. As the 100 GB replica volume is thin provisioned, 10% of the replica volume will be
reserved by default for thin provisioning. This yields a 10 GB current replica volume reserve (10% of 100
GB).
Total replica reserve is a percentage of current replica volume reserve. As the total replica reserve is 105%,
and the current replica volume reserve is 10 GB, 105% of 10 GB results in a 10.5 GB total replica reserve.
100% of the 10 GB (10GB) are in use in the current replica volume reserve, and a remaining 5% of the 10
GB (0.5 GB) is available for additional replicas in the total replica reserve.
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The secondary group is configured with 1 TB of delegated space for the primary group.
50 GB of data are written to the volume.
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A replica of the volume is created.
An additional 10 GB of data are written to the volume. There are now 60 GB of data in use.
The next attempt to replicate the volume is automatically paused with a critical alert, “Volume replication
paused because the replica reserve was exceeded. You must increase the replica reserve to resume
replication.”
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Writing 60 GB of data to the volume and creating replica changes the current replica volume reserve to 70
GB (60 GB of data + 10 GB of current replica volume reserve = 70 GB).
Total replica reserve is a percentage of current replica volume reserve. As the total replica reserve is 105%,
and the current replica volume reserve is 70 GB, 105% of 70 GB results approximately in a 74 GB Total
Replica Reserve. 100% of the 70 GB (70 GB) are in use in the current replica volume reserve, and an
additional 5% of the 70 GB (approximately 4 GB) is available for additional replicas in the total replica
reserve.
This means that 74 GB are reserved for replicas of the volume on the secondary group, and 70 GB of
those 74 GB are already in use by replicas of the volume. That leaves 4 GB of reserve space for the inprogress/paused replica. The current replication attempt of 10 GB is larger than 4 GB, and does not fit in
the replica reserve.
Even though there is plenty of delegated space and borrowable space on the secondary group, the
replication paused because active/in-progress replicas are not eligible to borrow space, and the amount of
changes in the replication attempt exceeded the available space in the total replica reserve. If there is
insufficient replica reserve on the secondary group, the system will require manual administrative
intervention to increase the amount of total replica reserve space to complete the replication.
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A
Additional resources
A.1
Technical support and customer service
Offering online and telephone-based support and service options, Dell support service can answer your
questions about PS Series arrays, groups, volumes, array software, and host software. Availability varies by
country and product, and some services might not be available in your area.
Visit Dell.com/support or call 800-945-3355 (United States and Canada).
For international support of Dell PS Series products, visit
http://www.dell.com/support/contents/us/en/555/article/Product-Support/Dell-Subsidiaries/equallogic
Note: If you do not have access to an Internet connection, contact information is printed on your
invoice, packing slip, bill, or Dell product catalog.
For PS Series software and documentation, visit eqlsupport.dell.com (login required).
A.2
Dell online services
Learn more about Dell products and services using this procedure:
1. Visit Dell.com or the URL specified in any Dell product information.
2. Use the locale menu or click on the link that specifies your country or region.
A.3
Dell PS Series storage solutions
To learn more about current and upcoming Dell PS Series solutions, visit the EqualLogic Dell TechCenter
page. Here you can find articles, demos, online discussions, technical documentation, and more details
about the PS Series product family.
For PS Series technical content, visit the EqualLogic Technical Content page on Dell TechCenter.
Dell Storage technical content can be found on the Storage Applications Engineering page.
A.4
Related documentation
See the following referenced or recommended resources related to this document.
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Dell EqualLogic Group Manager Administrator’s Manual at eqlsupport.dell.com (login required)
Dell EqualLogic Group Manager CLI Reference Guide at eqlsupport.dell.com (login required)
EqualLogic Snapshots and Clones: Best Practices and Sizing Guidelines on Dell TechCenter
Using Dell PS Series Asynchronous Replication on Dell TechCenter
Space Borrowing for Snapshots and Replicas | TR1084 | version 2